VANGUARD/PRIMECAP FUND INC
N-30D, 1999-08-18
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VANGUARD
PRIMECAP FUND

SEMIANNUAL
REPORT

JUNE 30, 1999

[A MEMBER OF THE VANGUARD GROUP (R) LOGO]

<PAGE>
AT VANGUARD, WE BELIEVE THAT TRADITION MATTERS

Our 9,000 crew members  embrace the  traditional  values on which our success is
built,  including integrity,  hard work, thrift,  teamwork,  and fair dealing on
behalf of our clients.

Our report cover pays homage to three anniversaries,  each of great significance
to The Vanguard Group:

o    The 200th  anniversary of the Battle of the Nile, which commenced on August
     1, 1798. HMS Vanguard,  the victorious British flagship at the Nile, is our
     namesake.  And its motto-- "Leading the way"--serves as a guiding principle
     for our company.

o    The 100th  birthday,  on July 23,  1998,  of Walter L.  Morgan,  founder of
     Wellington  Fund, the oldest member of what became The Vanguard Group.  Mr.
     Morgan was friend and mentor to Vanguard  founder John C. Bogle, and helped
     to shape the standards and business principles that Mr. Bogle laid down for
     Vanguard  at its  beginning  nearly 25 years  ago:  a stress  on  balanced,
     diversified  investments;  insistence  on  fair  dealing  and  candor  with
     clients; and a focus on long-term investing. To our great regret, Mr.Morgan
     died on September 2, 1998.

o    The 70th  anniversary,  on  December  28,  1998,  of the  incorporation  of
     Vanguard  Wellington  Fund. It is the nation's oldest balanced mutual fund,
     and one of only a handful  of funds  created in the 1920s that are still in
     operation.

Although Vanguard constantly tackles new challenges,  adopts new technology, and
develops new services,  we treasure the  traditions and values that set us apart
in a  crowded,  competitive  industry.  And we salute  our  shareholders,  whose
support and trust we strive to earn each and every day.

                                   [GRAPHIC]

                                    CONTENTS

                                  A MESSAGE TO
                                OUR SHAREHOLDERS
                                        1

                                 THE MARKETS IN
                                   PERSPECTIVE
                                        3

                                   REPORT FROM
                                   THE ADVISER
                                        5

                                   PERFORMANCE
                                     SUMMARY
                                        7

                                  FUND PROFILE
                                        8

                              FINANCIAL STATEMENTS
                                       10

                        All comparative mutual fund data
                         are from Lipper or Morningstar,
                             unless otherwise noted.
<PAGE>
FELLOW SHAREHOLDER,

[PHOTO]
John J. Brennan   John C. Bogle
Chairman & CEO    Senior Chairman

Vanguard  PRIMECAP Fund earned a stellar total return of +17.8% during the first
half of its fiscal  year,  which ended June 30, 1999,  outpacing by  substantial
margins the returns of its average peer and the Standard & Poor's 500 Index.

         The table below compares  PRIMECAP's  six-month  total return  (capital
change plus  reinvested  dividends) with those of the average growth mutual fund
and  the  S&P  500   Index,   which  is  a  widely   recognized   benchmark   of
large-capitalization  stocks.  The fund's  return is based on an increase in net
asset value from $47.66 per share on December 31,  1998,  to $55.47 per share on
June 30, 1999, and is adjusted for a  distribution  of $0.62 per share paid from
net realized capital gains.

- --------------------------------------------------------------------------------
                                                                 TOTAL RETURNS
                                                               SIX MONTHS ENDED
                                                                 JUNE 30, 1999
- --------------------------------------------------------------------------------
Vanguard PRIMECAP Fund                                                 +17.8%
- --------------------------------------------------------------------------------
Average Growth Fund                                                    +11.7%
- --------------------------------------------------------------------------------
S&P 500 Index                                                          +12.4%
- --------------------------------------------------------------------------------

FINANCIAL MARKETS IN REVIEW
The key  influences on financial  markets during the first half of 1999 were the
surprising  strength of the U.S.  economy's  long-running  expansion,  promising
corporate  earnings,  and  increasing  signs  that a  number  of  shaky  foreign
economies were on firmer footing. These factors were partly responsible for both
broad-based  gains in U.S.  stocks and increases in interest  rates,  which sent
bond prices lower.
         The U.S.  stock market,  as measured by the Wilshire 5000 Equity Index,
gained  +11.8%--equivalent to more than a full year's return based on historical
norms.  But the  half-year  saw a sharp  rotation in market  leadership.  As the
outlook for global economic  growth kept improving,  there was a notable revival
in cyclical  stocks--commodity-related  companies,  machinery makers,  and other
firms whose profit  prospects  are most closely  tied to the  economy's  ups and
downs.  This was a welcome change for cyclicals and other "value" stocks,  which
had lagged the  market  not just in the first  quarter  but for much of the last
five  years.  Within  the S&P  500  Index,  the  value  stocks--those  generally
characterized by above-average dividend yields and below-average  price/earnings
ratios--carried  the day during the second quarter and for the first half of the
year, when they gained +14.0% versus a gain of +11.0% for growth stocks.
         For bond investors,  a surging economy has a dark side: the possibility
that wage  pressures  and capacity  constraints  will push up  inflation,  which
diminishes  the buying  power of future bond  interest and  principal  payments.
After treading water in January,  interest rates rose throughout the rest of the
period.  And on the final day of the half-year,  the Federal Reserve Board hiked
its target for  short-term  interest  rates by 0.25% amid  concern  that  higher
inflation would be an inevitable  by-product of strong growth.  The yield of the
benchmark  30-year U.S.  Treasury  bond rose 86 basis  points  (0.86  percentage
point) on balance to end the six months at 5.96%. The Lehman Brothers  Aggregate
Bond Index, a proxy for the taxable U.S. bond market,  earned a negative  return
of -1.4% for the six  months,  as a price  decline  of -4.4%  engendered  by the
interest rate rise more than offset the +3.0% return from interest income.

                                       1
<PAGE>

PERFORMANCE OVERVIEW
Vanguard  PRIMECAP Fund's six-month  return of +17.8% was 6.1 percentage  points
above that of its average peer and 5.4 percentage points higher than that of the
S&P 500  Index.  This  outstanding  performance  was  the  result  of  excellent
investment management by our adviser,  PRIMECAP Management Company. A large part
of our advantage over the index came from the technology sector,  where the fund
has about  one-third  of its assets  invested,  compared  with about 17% for the
index.  The Report  From the  Adviser,  which  begins on page 5,  provides  more
details on the fund's holdings.
         The fund's relatively large stake in the producer durables group (about
14% of assets versus about 3% for the index) was also beneficial, as this sector
turned in the second-best  return among the industry groups in the index for the
half-year. The specific stocks chosen by the adviser enhanced the benefit of the
sector weighting.
         In achieving its fine  performance,  the fund overcame several negative
factors:  subpar  selections among stocks in the  consumer-discretionary  sector
(mainly  retailers)  and an average cash  position of roughly 7% (cash acts as a
drag on returns when stocks are rising). Especially notable is our surpassing of
the S&P 500  Index,  considering  that the  index  does  not hold  cash or incur
expenses, which all mutual funds must bear.
         While  PRIMECAP's   excellent  absolute  and  relative  performance  is
certainly  welcome,  keep in mind that a  double-digit  return  for a  six-month
period is well above what should be expected  from any  investment.  Also,  it's
important to remember that because  PRIMECAP  strives to outperform  the broader
market--by  emphasizing certain market sectors or particular companies from time
to time--its  returns  will often differ from those of broad market  benchmarks.
These  divergences  will sometimes be favorable,  as during the past six months,
and  sometimes  unfavorable,  as in 1998.  Overall,  we believe that  PRIMECAP's
skillful investment management and our significantly lower costs--our annualized
expense ratio is nearly 1 percentage point lower than that of the average growth
fund--are  important  advantages in our quest to provide  long-term returns that
surpass those of similar funds.

IN SUMMARY
Sticking with an investment  program  diversified  across  various asset classes
(stock funds,  bond funds,  and short-term  reserves) and market segments can be
trying at times,  particularly  when one  segment  runs  ahead of the others and
seems to be "the  only game in town."  But in the long run,  investors  are well
served by portfolios  constructed with the knowledge that market  leadership can
change abruptly and unpredictably.  So once you've decided on an investment plan
suited to your time horizon, goals, and tolerance for risk, we urge you to "stay
the course."
         We look forward to reporting to you on the full 1999 fiscal year in our
annual report six months hence.


/S/                      /S/
John C. Bogle            John J. Brennan
Senior Chairman          Chairman and
                         Chief Executive Officer
July 15, 1999

                                       2
<PAGE>

THE MARKETS IN PERSPECTIVE
SIX MONTHS ENDED JUNE 30, 1999

A markedly improved global economic outlook during the first half of 1999 led to
mostly positive stock market returns and lower bond prices.
         As the year began, many observers  expected that severe economic crises
in Asia,  Russia,  and some  Latin  American  nations  would  restrain  business
activity  worldwide,  even in the  United  States,  which  has been the  world's
economic  locomotive.  By spring,  however,  a  consensus  emerged  that  global
economic  activity  was  likely  to be  solid,  if not  robust.  This  change in
sentiment stemmed from several factors, including further vigorous growth in the
U.S.  economy,  a belief that Asia's slump had bottomed out, and moves in Europe
to ease monetary policy to encourage growth.
         Interest rates rose as investors  stopped wondering whether the Federal
Reserve  Board  would  lower  interest  rates--as  it had three  times in autumn
1998--and  began to wonder when the Fed would  increase rates to slow growth and
thereby forestall  inflation.  Indeed,  on the final day of the period,  the Fed
boosted  short-term  rates by 0.25 percentage  point.  In the stock market,  the
brighter  economic  outlook  led  to  a  change  in  leadership  from  glamorous
large-capitalization growth stocks to value stocks and small-cap stocks, both of
which had been among Wall Street's wallflowers in recent years.

U.S. STOCK MARKETS
The rise in stock prices  reflected the healthy  domestic  economy and improving
prospects  for  corporate  earnings.  The  overall  market,  as  measured by the
Wilshire 5000 Index,  rose 11.8% during the period,  while the S&P 500 Index,  a
yardstick for large-cap stocks, gained 12.4%.

- --------------------------------------------------------------------------------
                                                         TOTAL RETURNS
                                                 PERIODS ENDED JUNE 30, 1999
- --------------------------------------------------------------------------------
                                            6 MONTHS       1 YEAR       5 YEARS*
STOCKS
         S&P 500 Index                        12.4%         22.8%          27.9%
         Russell 2000 Index                    9.3           1.5           15.4
         Wilshire 5000 Index                  11.8          19.5           25.7
         MSCI EAFE Index                       4.1           7.9            8.5
- --------------------------------------------------------------------------------
BONDS
         Lehman Aggregate Bond Index          -1.4%          3.2%           7.8%
         Lehman 10 Year Municipal Bond Index  -1.7           2.3            6.8
         Salomon Smith Barney 3-Month
           U.S. Treasury Bill Index            2.2           4.7            5.2
- --------------------------------------------------------------------------------
OTHER
         Consumer Price Index                  1.4%          2.0%           2.3%
- --------------------------------------------------------------------------------
*Annualized.

         Large-cap  growth  stocks,   which  are  generally  perceived  as  less
vulnerable  than  other  stocks to  economic  slowdowns,  continued  to lead the
market's climb during the first quarter of the year.  During the second quarter,
however, value  stocks--especially  producers of commodity products such as oil,
aluminum,  and chemicals--moved to the front of the pack. Providing support were
generally  upbeat  corporate  profit  reports.   Indeed,   earnings  gains  were
sufficient to send prices higher  despite  rising  interest  rates,  which often
depress  stock  prices as well as bond prices.  For the six months,  the S&P 500
Index's  value stocks posted a 14.0% return while its growth stocks gained 11.0%
as a group.

                                       3
<PAGE>

         Small-cap stocks,  as measured by the Russell 2000 Index,  gained 9.3%,
although  that fact masks a  remarkable  turnaround:  Small-caps  declined  5.4%
during the first quarter of 1999, then advanced 15.6% during the second quarter.
Even so, the  cumulative  return of the  Russell  2000 over the past three years
lags the S&P 500 Index by nearly 80  percentage  points  (+37.6% for the Russell
2000 versus +115.2% for the S&P 500).
         Four of the top-performing  sectors within the S&P 500 Index during the
half-year  were solidly in the value  camp--the  "other  energy"  group  (+40%);
producer durables (+26%);  materials & processing  (+25%);  and  integrated-oils
(+17%). The strongest  growth-oriented  sector was the irrepressible  technology
group (+24%).  The poor performance of the consumer staples sector (-8%) was due
in part to the gains of the U.S. dollar against most foreign  currencies,  which
reduced the value of earnings from overseas operations.

U.S. BOND MARKETS
The powerful  economic  expansion that buoyed corporate profits and stock prices
was  too  much  of a  good  thing  for  the  bond  market.  Inflation  was  well
behaved--consumer  prices  rose 1.4% for the six  months and 2.0% for the twelve
months ended June 30--but investors and Fed policymakers  clearly were concerned
that an overheated economy might yet trigger significant  increases in wages and
overall prices.  Certainly,  there was no evidence of the "natural slowing" that
many  analysts  expected  for the  economy,  which is in the  longest  peacetime
expansion ever.
         Yields  on U.S.  Treasury  bonds  rose by  approximately  1  percentage
point--a  significant  rise for a  six-month  period.  The yield of the  30-year
Treasury bond rose 86 basis  points,  to 5.96% on June 30 from 5.10% on December
31, 1998. The yield of the 10-year Treasury rose 113 basis points, to 5.78% from
4.65%.  Money  market  rates  didn't  rise as far:  Yields  on  3-month  T-bills
increased on balance by only 33 basis points,  to 4.78% on June 30. Bond prices,
which move in the opposite  direction  from  interest  rates,  fell.  The Lehman
Aggregate Bond Index, a benchmark for investment-grade  taxable bonds,  declined
1.4% on a  total-return  basis,  as bond  prices  declined  an  average of 4.4%,
outweighing the 3.0% in interest income for the period.

INTERNATIONAL STOCK MARKETS
Led by sharp  recoveries  in stock  prices in Japan and many  emerging  markets,
international stock prices generated positive returns in local currencies during
the six  months.  However,  a  pervasive  rise in the  value of the U.S.  dollar
against other currencies reduced returns for U.S. investors (returns from abroad
are augmented when the dollar falls in value against other currencies).
         Overall, the developed markets outside the United States gained 4.1% in
U.S.-dollar  terms,  as measured  by the Morgan  Stanley  Capital  International
Europe,  Australasia,  Far East (EAFE) Index. The biggest  increases were in the
Pacific region--up 27.3% in local-currency terms and 21.1% when measured in U.S.
dollars.   Europe,  which  accounts  for  the  lion's  share  of  EAFE's  market
capitalization, was up 8.2% in local currencies. But in U.S. dollars, the return
from   European   stocks  was  a  negative   2.3%,   as   weakness  in  European
currencies--notably in the euro, the new 11-nation common  currency--lopped more
than 10  percentage  points  from the  local-currency  returns.  The MSCI Select
Emerging  Markets Free Index shot up 31.5% in dollar terms, led by Asian markets
that rebounded from severe losses suffered in 1997 and 1998.

                                       4
<PAGE>

REPORT FROM THE ADVISER

During the first half of 1999,  Vanguard  PRIMECAP  Fund's total return of 17.8%
exceeded  both the 12.4% return  recorded by the unmanaged S&P 500 Index and the
11.7% return of the average growth fund.
         As you may  recall,  the fund closed  1998 with an  exceptional  fourth
quarter--appreciating  28.8%.  In our  annual  report we cited  two  significant
developments that sparked the rally. First,  business activity in Southeast Asia
showed signs of recovery.  Second, market breadth improved as investors ventured
outside a relatively short list of the very largest-capitalization stocks. These
important  trends  persisted  throughout  the first  half of 1999,  providing  a
favorable  environment  for your  fund.  PRIMECAP  Fund holds the stocks of many
companies with significant Southeast Asian exposure, and our average holding has
a  substantially  smaller  market  cap than the  average  company in the S&P 500
Index.
         On the heels of a 57.5% gain in 1998, our technology holdings again led
the fund's  results in the first half of 1999.  Roughly  one-third of the fund's
assets are committed to this sector,  with particular emphasis on semiconductors
and  communications  equipment.  The outlook for the semiconductor  industry has
brightened markedly as the profusion of digital appliances continues. Orders are
picking up, lead times are  lengthening,  and excess capacity is being absorbed.
This results in much higher  profitability for this industry.  The stocks of LSI
Logic, Xilinx, and Texas Instruments led our semiconductor  holdings,  producing
gains of 186%, 76%, and 68%, respectively.
         Our  communications-equipment  stocks also enjoyed excellent returns in
the period.  Here,  the leading  manufacturers  are serving one of the  greatest
growth markets of this century.  The explosive growth of e-commerce and Internet
surfing has created a seemingly  insatiable  demand for network  infrastructure,
commonly referred to as bandwidth.  Also, continued  extraordinary growth in the
usage  of  various  wireless  communication  technologies  offers  unprecedented
opportunities  for equipment  providers.  Many of the premier  companies serving
these markets (Nokia,  Ericsson,  Motorola,  Nortel  Networks,  and Tellabs) are
significant  holdings for the fund. These five stocks,  which together represent
more than 10% of the fund's assets,  posted an average gain of nearly 64% during
the first half.
         The fund also enjoyed  strong  performances  from  technology  holdings
outside of the  semiconductor and  communications  arenas.  Specifically,  Adobe
Systems, Hewlett-Packard,  Sony, and the SABRE Group, which in aggregate account
for  approximately  10% of the  fund's  assets,  gained an  average of about 60%
during the six months.  Each of these four  companies is a leader in its market,
with strong brand identity and franchise value.

- --------------------------------------------------------------------------------
INVESTMENT PHILOSOPHY

The fund reflects a belief that  superior  long-term  investment  results can be
achieved by selecting stocks with prices lower than the fundamental value of the
underlying  companies,  based on the  investment  adviser's  assessment  of such
factors  as  their   industry   positions,   growth   potential,   and  expected
profitability.
- --------------------------------------------------------------------------------

         Although our exposure to the energy sector is small, our holdings there
performed  well.  Four of our five energy  stocks  (Burlington  Resources,  Pogo
Producing,  Schlumberger,  and Union Pacific Resources)

                                       5
<PAGE>

outperformed  the overall  market.  This sector had been out of favor for a long
time.  However,  our  interest in it increased as energy  prices  (adjusted  for
inflation) neared historic lows and valuations on the stocks became attractive.
         Following  a 69% gain in 1997 and a 53% gain in 1998,  our  holdings in
health care have  suffered  thus far in 1999.  Many of the major  pharmaceutical
companies  had  benefited  from the stock  market's  obsession  with the largest
growth stocks. As mentioned previously, this infatuation has waned, and the drug
stocks  were hurt in the  process.  Additionally,  talk of a  prescription  drug
benefit for Medicare patients has raised concern regarding the industry's future
profitability.  Our largest holding in the sector, Pharmacia & Upjohn, is one of
the smallest of the major pharmaceutical companies. Unlike most of its brethren,
Pharmacia  & Upjohn  has been a  relatively  poor  performer  over the last five
years. Two years ago, new management joined the company and moved quickly to cut
costs and increase operational productivity. The company is well positioned with
several new drugs and has few products that will be losing patent  protection in
the near term. The company has a promising  pipeline of products in development,
especially  the lead compound in the first new class of antibiotics in 30 years.
We believe the growth and profitability of Pharmacia & Upjohn over the next five
years can be dramatically better than industry observers expect.
         Within  the  health-care  sector,  we  have  marginally  increased  our
commitment to biotechnology  stocks. In our opinion, over the last few years the
viability of this industry has clearly been  validated.  Many of these companies
have exciting  products in the pipeline,  with multiple  compounds in late-stage
clinical trials. They have secured distribution by forging partnerships with the
major drug companies. They are also serving as important components of the major
pharmaceutical  companies'   research-and-development   efforts,   receiving  in
exchange   funding  and  royalties  on  future  product  sales.   Despite  these
attributes,  the stocks generally sell at a material  discount to the valuations
accorded the more traditional drug companies.
         Finally,  our significant  overweighting in the  transportation  sector
provided a modest  increment to our  performance  during the first half of 1999.
Performance  within the industry and among our holdings was mixed.  For example,
among the airlines,  Southwest  Airlines and AMR surpassed the market  averages,
gaining 37% and 15%, respectively.  However, Delta Air Lines and UAL trailed the
averages.  Similarly,  in the airfreight category, FDX gained an impressive 22%,
but Airborne Freight declined 23%.
         We expect the  market's  expanding  breadth to continue and business in
Asia to  steadily  improve.  In such  an  environment,  we  believe  the  fund's
performance relative to its benchmarks should be favorable.

Howard B. Schow, Portfolio Manager       Theo A. Kolokotrones, Portfolio Manager

Joel P. Fried, Assistant Portfolio       F. Jack Liebau Jr., Assistant Portfolio
Manager                                  Manager


PRIMECAP Management Company

July 9, 1999

                                       6
<PAGE>
PERFORMANCE SUMMARY
PRIMECAP FUND

All of the data on this page represent past performance, which cannot be used to
predict  future returns that may be achieved by the fund.  Note,  too, that both
share price and return can fluctuate  widely, so an investment in the fund could
lose money.

TOTAL INVESTMENT RETURNS: NOVEMBER 1, 1984-JUNE 30, 1999
- --------------------------------------------------------------------------------
                           PRIMECAP FUND                              S&P 500
FISCAL          CAPITAL        INCOME         TOTAL                   TOTAL
YEAR            RETURN         RETURN         RETURN                  RETURN
- --------------------------------------------------------------------------------
1984              4.9%           0.0%           4.9%                    0.6%
1985             35.6            0.2           35.8                    31.8
1986             21.8            1.7           23.5                    18.7
1987             -3.2            0.9           -2.3                     5.3
1988             13.7            1.0           14.7                    16.6
1989             20.2            1.4           21.6                    31.7
1990             -3.8            1.0           -2.8                    -3.1
1991             31.8            1.3           33.1                    30.5
- --------------------------------------------------------------------------------
                           PRIMECAP FUND                              S&P 500
FISCAL          CAPITAL        INCOME         TOTAL                   TOTAL
YEAR            RETURN         RETURN         RETURN                  RETURN
- --------------------------------------------------------------------------------
1992              8.2%           0.8%           9.0%                    7.6%
1993             17.6            0.4           18.0                    10.1
1994             10.7            0.7           11.4                     1.3
1995             34.4            1.1           35.5                    37.6
1996             17.5            0.8           18.3                    23.0
1997             36.1            0.7           36.8                    33.4
1998             24.5            0.9           25.4                    28.6
1999*            17.8            0.0           17.8                    12.4
- --------------------------------------------------------------------------------
*Six months ended June 30, 1999.
See  Financial  Highlights  table  on page 14 for  dividend  and  capital  gains
information for the past five years.

AVERAGE ANNUAL TOTAL RETURNS: PERIODS ENDED JUNE 30, 1999
- --------------------------------------------------------------------------------
                                                             10 YEARS
                  INCEPTION                         ----------------------------
                    DATE       1 YEAR     5 YEARS    CAPITAL    INCOME    TOTAL
- --------------------------------------------------------------------------------
PRIMECAP Fund     11/1/1984    32.06%     29.16%     19.65%     0.92%     20.57%
- --------------------------------------------------------------------------------


                                       7
<PAGE>

FUND PROFILE
PRIMECAP FUND

This Profile  provides a snapshot of the fund's  characteristics  as of June 30,
1999,  compared where  appropriate to an unmanaged  index.  Key elements of this
Profile are defined on page 9.

PORTFOLIO CHARACTERISTICS
- --------------------------------------------------------------------------------
                                           PRIMECAP                      S&P 500
- --------------------------------------------------------------------------------
Number of Stocks                              106                            500
Median Market Cap                          $15.5B                         $70.1B
Price/Earnings Ratio                        23.4x                          29.6x
Price/Book Ratio                             3.8x                           5.2x
Yield                                        0.3%                           1.2%
Return on Equity                            18.5%                          22.4%
Earnings Growth Rate                        10.7%                          14.8%
Foreign Holdings                             6.6%                           1.6%
Turnover Rate                                16%*                             --
Expense Ratio                              0.53%*                             --
Cash Reserves                                7.0%                             --

*Annualized.

VOLATILITY MEASURES
- --------------------------------------------------------------------------------
                                           PRIMECAP                      S&P 500
- --------------------------------------------------------------------------------
R-Squared                                    0.85                          1.00
Beta                                         1.07                          1.00

INVESTMENT FOCUS
- --------------------------------------------------------------------------------
STYLE - GROWTH
MARKET CAP - MEDIUM

TEN LARGEST HOLDINGS (% OF TOTAL NET ASSETS)
- --------------------------------------------------------------------------------
Texas Instruments, Inc.                                                     7.3%
FDX Corp.                                                                   5.1
AMR Corp.                                                                   3.8
Delta Air Lines, Inc.                                                       3.7
Pharmacia & Upjohn, Inc.                                                    3.4
Motorola, Inc.                                                              3.4
Guidant Corp.                                                               3.2
Nortel Networks Corp.                                                       3.2
Intel Corp.                                                                 3.2
Micron Technology, Inc.                                                     3.2
- --------------------------------------------------------------------------------
Top Ten                                                                    39.5%

SECTOR DIVERSIFICATION (% OF COMMON STOCKS)
- --------------------------------------------------------------------------------
                                     JUNE 30, 1998            JUNE 30, 1999
                                     -------------------------------------------
                                       PRIMECAP         PRIMECAP         S&P 500
                                     -------------------------------------------
Auto & Transportation ................  18.0%            18.1%              2.5%
Consumer Discretionary ...............  10.5              5.2              12.8
Consumer Staples .....................   2.1              0.4               7.8
Financial Services ...................   6.7              1.4              16.5
Health Care ..........................  11.9             13.7              11.1
Integrated Oils ......................   0.0              0.0               5.1
Other Energy .........................   2.8              2.6               1.4
Materials & Processing ...............   6.9              4.3               3.5
Producer Durables ....................   8.2             11.5               3.5
Technology ...........................  32.0             36.7              18.9
Utilities ............................   0.0              0.0              11.3
Other ................................   0.9              6.1               5.6

                                       8
<PAGE>

BETA. A measure of the magnitude of a fund's past  share-price  fluctuations  in
relation  to the ups and downs of the  overall  market  (or  appropriate  market
index).  The market (or index) is assigned a beta of 1.00, so a fund with a beta
of 1.20  would have seen its share  price  rise or fall by 12% when the  overall
market rose or fell by 10%.

CASH  RESERVES.  The  percentage  of a  fund's  net  assets  invested  in  "cash
equivalents"--highly  liquid,  short-term,   interest-bearing  securities.  This
figure does not include cash  invested in futures  contracts  to simulate  stock
investment.

EARNINGS  GROWTH RATE.  The average  annual rate of growth in earnings  over the
past five years for the stocks now in a fund.

EXPENSE  RATIO.  The  percentage of a fund's  average net assets used to pay its
annual  administrative  and advisory  expenses.  These expenses  directly reduce
returns to investors.

FOREIGN HOLDINGS. The percentage of a fund's equity assets represented by stocks
or American Depositary Receipts of companies based outside the United States.

INVESTMENT  FOCUS.  This  grid  indicates  the  focus  of a fund in terms of two
attributes:  market  capitalization  (large,  medium,  or  small)  and  relative
valuation (growth, value, or a blend).

MEDIAN  MARKET  CAP.  An  indicator  of the  size of  companies  in which a fund
invests;  the  midpoint  of  market   capitalization   (market  price  x  shares
outstanding) of a fund's stocks, weighted by the proportion of the fund's assets
invested  in each  stock.  Stocks  representing  half of the fund's  assets have
market capitalizations above the median, and the rest are below it.

NUMBER OF STOCKS. An indicator of diversification. The more stocks a fund holds,
the more  diversified  it is and the more  likely  to  perform  in line with the
overall stock market.

PRICE/BOOK  RATIO.  The share price of a stock divided by its net worth, or book
value,  per share.  For a fund,  the weighted  average  price/book  ratio of the
stocks it holds.

PRICE/EARNINGS  RATIO.  The ratio of a stock's  current  price to its  per-share
earnings over the past year. For a fund, the weighted  average P/E of the stocks
it holds. P/E is an indicator of market expectations about corporate  prospects;
the higher the P/E, the greater the expectations for a company's future growth.

R-SQUARED.  A measure of how much of a fund's past  returns can be  explained by
the returns from the overall market (or its benchmark  index). If a fund's total
return  were  precisely  synchronized  with the  overall  market's  return,  its
R-squared  would  be 1.00.  If a  fund's  returns  bore no  relationship  to the
market's returns, its R-squared would be 0.

RETURN ON  EQUITY.  The annual  average  rate of return  generated  by a company
during the past five years for each dollar of  shareholder's  equity (net income
divided by  shareholder's  equity).  For a fund, the weighted  average return on
equity for the companies whose stocks it holds.

SECTOR DIVERSIFICATION. The percentages of a fund's common stocks that come from
each of the major industry groups that compose the stock market.

TEN LARGEST  HOLDINGS.  The percentage of net assets that a fund has invested in
its ten largest holdings.  (The average for stock mutual funds is about 30%.) As
this percentage  rises, a fund's returns are likely to be more volatile  because
they are more dependent on the fortunes of a few companies.

TURNOVER RATE. An indication of trading  activity during the period.  Funds with
high  turnover  rates  incur  higher  transaction  costs and are more  likely to
distribute capital gains (which are taxable to investors).

YIELD.  A snapshot of a fund's  income from interest and  dividends.  The yield,
expressed  as a  percentage  of the fund's net asset  value,  is based on income
earned over the past 30 days and is  annualized,  or  projected  forward for the
coming  year.  The  index  yield  is  based on the  current  annualized  rate of
dividends paid on stocks in the index.

                                       9
<PAGE>

FINANCIAL STATEMENTS
JUNE 30, 1999 (UNAUDITED)

STATEMENT OF NET ASSETS
This Statement  provides a detailed list of the fund's holdings,  including each
security's market value on the last day of the reporting period.  Securities are
grouped  and  subtotaled  by asset  type  (common  stocks,  bonds,  etc.) and by
industry sector. Other assets are added to, and liabilities are subtracted from,
the value of Total Investments to calculate the fund's Net Assets.  Finally, Net
Assets are divided by the outstanding  shares of the fund to arrive at its share
price, or Net Asset Value (NAV) Per Share.
         At the  end of the  Statement  of Net  Assets,  you  will  find a table
displaying  the  composition  of the  fund's  net  assets  on both a dollar  and
per-share  basis.  Because all income and any realized gains must be distributed
to  shareholders  each year, the bulk of net assets  consists of Paid in Capital
(money  invested by  shareholders).  The  amounts  shown for  Undistributed  Net
Investment  Income and  Accumulated  Net Realized Gains usually  approximate the
sums the fund had available to distribute to shareholders as income dividends or
capital gains as of the statement date. Any Accumulated Net Realized Losses, and
any cumulative  excess of  distributions  over net income or net realized gains,
will appear as negative balances.  Unrealized Appreciation (Depreciation) is the
difference  between the market value of the fund's  investments  and their cost,
and reflects the gains  (losses) that would be realized if the fund were to sell
all of its investments at their statement-date values.
- --------------------------------------------------------------------------------
                                                                          MARKET
                                                                          VALUE*
PRIMECAP FUND                                        SHARES                (000)
- --------------------------------------------------------------------------------
COMMON STOCKS (93.0%)
- --------------------------------------------------------------------------------
AUTO & TRANSPORTATION (16.8%)
o        FDX Corp.                               13,146,000          $  713,171
o(1)     AMR Corp.                                7,700,000             525,525
(1)      Delta Air Lines, Inc.                    8,800,000             507,100
         Southwest Airlines Co.                   8,705,500             270,959
o        UAL Corp.                                2,300,000             149,500
(1)      Airborne Freight Corp.                   3,400,000              94,138
         Fleetwood Enterprises, Inc.              1,680,600              44,431
         Arvin Industries, Inc.                     780,000              29,542
                                                                      ----------
                                                                      2,334,366
                                                                      ----------
CONSUMER DISCRETIONARY (4.8%)
o        Costco Cos., Inc.                        2,400,000             192,150
(1)      Harcourt General, Inc.                   3,132,200             161,504
o(1)     Neiman Marcus Group Inc.                 3,152,600              80,982
         Manpower Inc.                            2,720,000              61,540
         Dillard's Inc.                           1,241,500              43,608
(1)      The McClatchy Co. Class A                1,000,000              33,125
         Lowe's Cos., Inc.                          438,000              24,829
o        PETsMART, Inc.                           1,930,000              19,782
         Dayton Hudson Corp.                        190,000              12,350
         Block Drug Co. Class A                     278,100              11,593
         NIKE, Inc. Class B                         176,000              11,143
o        GC Cos.                                    200,000               7,150
         The Gap, Inc.                              108,750               5,478
         Mattel, Inc.                               100,000               2,644
o        Filene's Basement Corp.                    985,000               1,416
                                                                      ----------
                                                                        669,294
                                                                      ----------
CONSUMER STAPLES (0.4%)
         Brown-Forman Corp. Class B                 800,000              52,150
                                                                      ----------
- --------------------------------------------------------------------------------
                                                                          MARKET
                                                                          VALUE*
                                                     SHARES                (000)
- --------------------------------------------------------------------------------
ENERGY (2.4%)
         Schlumberger Ltd.                        1,293,500              82,380
         Burlington Resources, Inc.               1,887,300              81,626
         Union Pacific Resources Group, Inc.      3,900,000              63,619
         Noble Affiliates, Inc.                   2,100,000              59,194
(1)      Pogo Producing Co.                       2,600,000              48,425
                                                                      ----------
                                                                        335,244
                                                                      ----------
FINANCIAL SERVICES (1.3%)
         Torchmark Corp.                          2,600,000              88,725
         Transatlantic Holdings, Inc.               562,500              42,152
         St. Paul Cos., Inc.                      1,100,000              34,994
         City National Corp.                        312,785              11,710
         American International Group, Inc.          40,692               4,763
                                                                      ----------
                                                                        182,344
                                                                      ----------
HEALTH CARE (12.7%)
         Pharmacia & Upjohn, Inc.                 8,397,900             477,106
         Guidant Corp.                            8,621,264             443,456
o(1)     Centocor, Inc.                           5,940,500             276,976
         PE Corp.-PE Biosystems Group             1,300,000             149,175
         Medtronic, Inc.                          1,620,000             126,158
         Johnson & Johnson                        1,100,000             107,800
o        Boston Scientific Corp.                  2,000,000              87,875
         Novartis AG ADR                            755,000              56,059
         Eli Lilly & Co.                            546,640              39,153
o        Biogen, Inc.                                34,600               2,225
o        BioChem Pharma Inc.                         38,200                 716
                                                                      ----------
                                                                      1,766,699
                                                                      ----------
                                       10
<PAGE>

- --------------------------------------------------------------------------------
                                                                          MARKET
                                                                          VALUE*
                                                     SHARES                (000)
- --------------------------------------------------------------------------------
MATERIALS & PROCESSING (4.0%)
         Engelhard Corp.                          5,200,000             117,650
         Potash Corp. of Saskatchewan, Inc.       1,800,000              93,150
         Temple-Inland Inc.                       1,300,000              88,725
(1)      MacDermid, Inc.                          1,701,000              79,097
         Sigma-Aldrich Corp.                      2,000,000              68,875
(1)      Granite Construction Co.                 2,100,000              61,556
         OM Group, Inc.                           1,140,000              39,330
         Stepan Co.                                 134,200               3,405
                                                                      ----------
                                                                        551,788
                                                                      ----------
PRODUCER DURABLES (10.7%)
         Nortel Networks Corp.                    5,087,300             441,641
         Pitney Bowes, Inc.                       2,400,000             154,200
         Caterpillar, Inc.                        2,470,000             148,200
(1)      Millipore Corp.                          2,820,000             114,386
o(1)     Plantronics, Inc.                        1,608,000             104,721
(1)      Tektronix, Inc.                          3,400,000             102,638
         Deere & Co.                              2,350,000              93,119
o        Lexmark International Group,Inc.Class A  1,400,000              92,487
o        Nokia Corp. ADR                            800,000              73,250
o        Dionex Corp.                             1,020,000              41,310
         Kennametal, Inc.                         1,260,000              39,060
         Donaldson Co., Inc.                      1,080,000              26,460
         Belden, Inc.                               702,400              16,814
         Pall Corp.                                 750,000              16,641
o        PE Corp.-Celera Genomics Group             650,000              10,522
         Molex, Inc.                                195,312               7,227
         Molex, Inc. Class A                        195,312               6,152
                                                                      ----------
                                                                      1,488,828
                                                                      ----------
TECHNOLOGY (34.2%)
         COMMUNICATIONS TECHNOLOGY (7.1%)
         Motorola, Inc.                           4,981,850             472,030
         LM Ericsson Telephone Co.ADR Class B     9,200,000             303,025
o        Tellabs, Inc.                            2,400,000             162,150
         Corning, Inc.                              600,000              42,075
         LM Ericsson Telephone Co. 4.25 % Cvt. Pfd. 620,000               5,386

         COMPUTER SERVICES, SOFTWARE & SYSTEM (4.2%)
(1)      Adobe Systems, Inc.                      5,190,000             426,391
o(1)     The SABRE Group Holdings, Inc.           2,309,200             158,758
o        Tripos Inc.                                 95,000                 784

         COMPUTER TECHNOLOGY (4.0%)
         Hewlett-Packard Co.                      3,930,000             394,965
         Compaq Computer Corp.                    6,228,925             147,548
o(1)     Evans & Sutherland Computer Corp.          840,000              10,972

ELECTRONICS (2.4%)
         Sony Corp. ADR                           3,019,000             333,222

         ELECTRONICS--SEMICONDUCTORS/COMPONENTS (15.6%)
         Texas Instruments, Inc.                  6,990,000           1,013,550
         Intel Corp.                              7,390,000             439,705
o        Micron Technology, Inc.                 10,900,000             439,406

- --------------------------------------------------------------------------------
                                                                          MARKET
                                                                          VALUE*
PRIMECAP FUND                                        SHARES                (000)
- --------------------------------------------------------------------------------
o        Xilinx, Inc.                             3,400,000             194,650
o        LSI Logic Corp.                          1,488,700              68,666

         ELECTRONICS--TECHNOLOGY (0.9%)
         Symbol Technologies, Inc.                2,400,000              88,500
o(1)     Coherent, Inc.                           1,800,000              33,525
                                                                      ----------
                                                                      4,735,308
                                                                      ----------
OTHER (5.7%)
         The Seagram Co. Ltd.                     3,100,000             156,163
         Miscellaneous (4.5%)                                           629,895
                                                                      ----------
                                                                        786,058
                                                                      ----------
- --------------------------------------------------------------------------------
TOTAL COMMON STOCKS
         Cost $6,996,543)                                             12,902,079
- --------------------------------------------------------------------------------
                                                       FACE
                                                     AMOUNT
                                                      (000)
- --------------------------------------------------------------------------------
TEMPORARY CASH INVESTMENTS (7.0%)
- --------------------------------------------------------------------------------
REPURCHASE AGREEMENTS
Collateralized by U.S. Government
     Obligations in a Pooled
     Cash Account
     4.87%, 7/1/1999                               $967,160             967,160
     4.96%, 7/1/1999--Note G                          3,480               3,480
- --------------------------------------------------------------------------------
TOTAL TEMPORARY CASH INVESTMENTS
     (Cost $970,640)                                                    970,640
- --------------------------------------------------------------------------------
TOTAL INVESTMENTS (100.0%)
     (Cost $7,967,183)                                               13,872,719
- --------------------------------------------------------------------------------
OTHER ASSETS AND LIABILITIES
- --------------------------------------------------------------------------------
Other Assets--Note C                                                     56,630
Liabilities--Note G                                                     (53,745)
                                                                      ----------
                                                                          2,885
- --------------------------------------------------------------------------------
NET ASSETS (100%)
- --------------------------------------------------------------------------------
Applicable to 250,134,503 outstanding
     $.001 par value shares of beneficial
     interest (unlimited authorization)                             $13,875,604
================================================================================
NET ASSET VALUE PER SHARE                                                $55.47
================================================================================
  *See Note A in Notes to Financial Statements.
  oNon-Income-Producing Security.
  (1)Considered an affiliated  company  as the  fund  owns  more  than 5% of the
     outstanding  voting  securities of such company.  The total market value of
     investments in affiliated companies was $2,820,000,000.
  ADR--American Depositary Receipt.
- --------------------------------------------------------------------------------
AT JUNE 30, 1999, NET ASSETS CONSISTED OF:
- --------------------------------------------------------------------------------
                                                       Amount               Per
                                                        (000)             Share
- --------------------------------------------------------------------------------
Paid in Capital                                7,345,493                 $29.37
Undistributed Net
  Investment Income                               23,516                    .09
Accumulated Net
  Realized Gains                                 601,059                   2.40
Unrealized Appreciation--
  Note F                                       5,905,536                  23.61
- --------------------------------------------------------------------------------
NET ASSETS                                   $13,875,604                 $55.47
================================================================================

                                       11
<PAGE>

STATEMENT OF OPERATIONS
This Statement  shows dividend and interest income earned by the fund during the
reporting period,  and details the operating expenses charged to the fund. These
expenses  directly  reduce the amount of investment  income  available to pay to
shareholders  as  dividends.  This  Statement  also  shows  any Net Gain  (Loss)
realized  on the  sale of  investments,  and the  increase  or  decrease  in the
Unrealized Appreciation (Depreciation) on investments during the period.
<TABLE>
<CAPTION>

- ---------------------------------------------------------------------------------------
                                                                          PRIMECAP FUND
                                                         SIX MONTHS ENDED JUNE 30, 1999
                                                                                  (000)
- ---------------------------------------------------------------------------------------
INVESTMENT INCOME
INCOME
<S>                                                                         <C>
         Dividends*                                                         $   35,514
         Interest                                                               23,649
         Security Lending                                                          494
                                                                             ----------
                  Total Income                                                  59,657
EXPENSES                                                                     ----------
         Investment Advisory Fees--Note B                                       12,256
         The Vanguard Group--Note C
                  Management and Administrative                                 19,431
                  Marketing and Distribution                                     1,038
         Custodian Fees                                                              7
         Auditing Fees                                                               8
         Shareholders' Reports                                                     336
         Trustees' Fees and Expenses                                                10
                                                                             ----------
                  Total Expenses                                                33,086
                  Expenses Paid Indirectly--Note D                                  (4)
                                                                             ----------
                  Net Expenses                                                  33,082
- ---------------------------------------------------------------------------------------
NET INVESTMENT INCOME                                                           26,575
- ---------------------------------------------------------------------------------------
REALIZED NET GAIN ON INVESTMENT SECURITIES SOLD                                602,043
- ---------------------------------------------------------------------------------------
CHANGE IN UNREALIZED APPRECIATION (DEPRECIATION) OF INVESTMENT SECURITIES    1,431,500
- ---------------------------------------------------------------------------------------
NET INCREASE IN NET ASSETS RESULTING FROM OPERATIONS                        $2,060,118
=======================================================================================
*Dividend income from affiliated companies was $4,835,000.
</TABLE>

                                       12
<PAGE>
STATEMENT OF CHANGES IN NET ASSETS
This Statement shows how the fund's total net assets changed during the two most
recent reporting periods. The Operations section summarizes information detailed
in  the  Statement  of  Operations.   The  amounts  shown  as  Distributions  to
shareholders  from the fund's net  income  and  capital  gains may not match the
amounts shown in the Operations section, because distributions are determined on
a tax  basis  and may be made in a period  different  from the one in which  the
income was earned or the gains were  realized on the financial  statements.  The
Capital Share Transactions section shows the amount shareholders invested in the
fund,  either by purchasing shares or by reinvesting  distributions,  as well as
the amounts redeemed.  The  corresponding  numbers of Shares Issued and Redeemed
are shown at the end of the Statement.
<TABLE>
<CAPTION>
- ------------------------------------------------------------------------------------------------------------------------
                                                                                                  PRIMECAP FUND
                                                                                ----------------------------------------
                                                                                      SIX MONTHS                    YEAR
                                                                                           ENDED                   ENDED
                                                                                   JUN. 30, 1999           DEC. 31, 1998
                                                                                           (000)                   (000)
- ------------------------------------------------------------------------------------------------------------------------
INCREASE (DECREASE) IN NET ASSETS
OPERATIONS
<S>                                                                                       <C>                    <C>
         Net Investment Income                                                       $    26,575            $    76,585
         Realized Net Gain                                                               602,043                433,652
         Change in Unrealized Appreciation (Depreciation)                              1,431,500              1,697,719
                                                                                ----------------------------------------
                  Net Increase in Net Assets Resulting from Operations                 2,060,118              2,207,956
                                                                                ----------------------------------------
DISTRIBUTIONS
         Net Investment Income                                                                --                (80,088)
         Realized Capital Gain                                                          (150,153)              (348,822)
                                                                                ----------------------------------------
                  Total Distributions                                                   (150,153)              (428,910)
                                                                                ----------------------------------------
CAPITAL SHARE TRANSACTIONS1
         Issued                                                                        1,350,409              3,038,897
         Issued in Lieu of Cash Distributions                                            146,718                418,210
         Redeemed                                                                       (741,374)            (2,212,430)
                                                                                ----------------------------------------
                  Net Increase from Capital Share Transactions                           755,753              1,244,677
- ------------------------------------------------------------------------------------------------------------------------
         Total Increase                                                                2,665,718              3,023,723
- ------------------------------------------------------------------------------------------------------------------------
NET ASSETS
         Beginning of Period                                                          11,209,886              8,186,163
                                                                                ----------------------------------------
         End of Period                                                               $13,875,604            $11,209,886
========================================================================================================================
1Shares Issued (Redeemed)
         Issued                                                                           26,511                 71,476
         Issued in Lieu of Cash Distributions                                              2,967                  9,174
         Redeemed                                                                        (14,553)               (52,348)
                                                                                ----------------------------------------
                  Net Increase in Shares Outstanding                                      14,925                 28,302
========================================================================================================================
</TABLE>

                                       13
<PAGE>

FINANCIAL HIGHLIGHTS
This table  summarizes  the  fund's  investment  results  and  distributions  to
shareholders on a per-share  basis. It also presents the fund's Total Return and
shows net  investment  income and expenses as percentages of average net assets.
These data will help you assess:  the  variability  of the fund's net income and
total returns from year to year;  the relative  contributions  of net income and
capital gains to the fund's total return; how much it costs to operate the fund;
and the extent to which the fund tends to distribute  capital  gains.  The table
also  shows the  Portfolio  Turnover  Rate,  a measure of  trading  activity.  A
turnover  rate of 100% means that the  average  security is held in the fund for
one year.
<TABLE>
<CAPTION>
- -----------------------------------------------------------------------------------------------------------------------------
                                                                                          PRIMECAP FUND
                                                                                    YEAR ENDED DECEMBER 31,
                                                                 ------------------------------------------------------------

FOR A SHARE OUTSTANDING                      SIX MONTHS ENDED
THROUGHOUT EACH PERIOD                          JUNE 30, 1999        1998       1997         1996         1995          1994
- -----------------------------------------------------------------------------------------------------------------------------
<S>                                                    <C>         <C>        <C>          <C>          <C>           <C>
NET ASSET VALUE, BEGINNING OF PERIOD                   $47.66      $39.56     $30.08       $26.23       $19.98        $18.42
- -----------------------------------------------------------------------------------------------------------------------------
INVESTMENT OPERATIONS
         Net Investment Income                            .10         .34        .21          .19          .22           .12
         Net Realized and Unrealized Gain (Loss)
                  on Investments                         8.33        9.63      10.77         4.59         6.84          1.97
                                                  ---------------------------------------------------------------------------
                  Total from Investment Operations       8.43        9.97      10.98         4.78         7.06          2.09
                                                  ---------------------------------------------------------------------------
DISTRIBUTIONS
         Dividends from Net Investment Income             --         (.35)      (.20)        (.20)        (.22)         (.12)
         Distributions from Realized Capital Gains       (.62)      (1.52)     (1.30)        (.73)        (.59)         (.41)
                                                  ---------------------------------------------------------------------------
                  Total Distributions                    (.62)      (1.87)     (1.50)        (.93)        (.81)         (.53)
- -----------------------------------------------------------------------------------------------------------------------------
NET ASSET VALUE, END OF PERIOD                         $55.47      $47.66     $39.56       $30.08       $26.23        $19.98
=============================================================================================================================
TOTAL RETURN                                           17.85%       25.44%    36.79%       18.31%       35.48%        11.41%
=============================================================================================================================
RATIOS/SUPPLEMENTAL DATA
         Net Assets, End of Period (Millions)         $13,876     $11,210     $8,186       $4,204       $3,237        $1,554
         Ratio of Total Expenses to
                  Average Net Assets                   0.53%*       0.51%      0.51%        0.59%        0.58%         0.64%
RATIO OF NET INVESTMENT
INCOME TO AVERAGE NET ASSETS                           0.43%*       0.78%      0.69%        0.69%        0.99%         0.79%
         Portfolio Turnover Rate                         16%*         13%        13%          10%           7%            8%
=============================================================================================================================
*Annualized.
</TABLE>
                                       14
<PAGE>

NOTES TO FINANCIAL STATEMENTS
Vanguard PRIMECAP Fund is registered under the Investment Company Act of 1940 as
a diversified open-end investment company, or mutual fund.

A. The following  significant  accounting policies conform to generally accepted
accounting  principles  for mutual  funds.  The fund  consistently  follows such
policies in preparing its financial statements.
         1.  SECURITY  VALUATION:  Equity  securities  are  valued at the latest
quoted  sales  prices as of the close of trading on the New York Stock  Exchange
(generally  4:00 p.m.  Eastern time) on the valuation  date; such securities not
traded on the valuation date are valued at the mean of the latest quoted bid and
asked  prices.  Prices are taken from the primary  market in which each security
trades. Temporary cash investments are valued at cost, which approximates market
value.  Securities  for which market  quotations  are not readily  available are
valued by methods deemed by the Board of Trustees to represent fair value.
         2. FEDERAL  INCOME TAXES:  The fund intends to continue to qualify as a
regulated   investment  company  and  distribute  all  of  its  taxable  income.
Accordingly,  no provision for federal income taxes is required in the financial
statements.
         3.  REPURCHASE  AGREEMENTS:  The fund,  along with other members of The
Vanguard  Group,  transfers  uninvested  cash balances to a Pooled Cash Account,
which  is  invested  in  repurchase   agreements  secured  by  U.S.   government
securities.  Securities pledged as collateral for repurchase agreements are held
by a custodian bank until the agreements  mature.  Each agreement  requires that
the market value of the  collateral be sufficient to cover  payments of interest
and principal; however, in the event of default or bankruptcy by the other party
to  the  agreement,  retention  of  the  collateral  may  be  subject  to  legal
proceedings.
         4.  DISTRIBUTIONS: Distributions to shareholders are  recorded  on  the
ex-dividend date.
         5. OTHER: Dividend income is recorded on the ex-dividend date. Security
transactions  are accounted for on the date securities are bought or sold. Costs
used to determine  realized gains (losses) on the sale of investment  securities
are those of the specific securities sold.

B. PRIMECAP Management Company provides investment advisory services to the fund
for a fee calculated at an annual percentage rate of average net assets. For the
six months ended June 30, 1999, the advisory fee represented an effective annual
rate of 0.20% of the fund's average net assets.

C. The Vanguard Group  furnishes at cost corporate  management,  administrative,
marketing,  and distribution  services. The costs of such services are allocated
to the fund  under  methods  approved  by the  Board of  Trustees.  The fund has
committed to provide up to 0.40% of its net assets in capital  contributions  to
Vanguard.  At June 30, 1999, the fund had  contributed  capital of $1,982,000 to
Vanguard (included in Other Assets), representing 0.01% of the fund's net assets
and 2.8% of Vanguard's capitalization. The fund's Trustees and officers are also
Directors and officers of Vanguard.

D. The  fund's  custodian  bank has  agreed  to  reduce  its fees  when the fund
maintains cash on deposit in the  non-interest-bearing  custody account. For the
six months  ended June 30,  1999,  custodian  fee  offset  arrangements  reduced
expenses by $4,000.

E. During the six months ended June 30, 1999, the fund purchased  $1,256,289,000
of investment securities and sold $901,486,000 of investment  securities,  other
than temporary cash investments.

F. At June 30, 1999, net unrealized  appreciation  of investment  securities for
financial   reporting  and  federal  income  tax  purposes  was  $5,905,536,000,
consisting of unrealized gains of $6,163,178,000 on securities that had risen in
value since their purchase and  $257,642,000 in unrealized  losses on securities
that had fallen in value since their purchase.

                                       15
<PAGE>
NOTES TO FINANCIAL STATEMENTS (CONTINUED)

G. The market value of  securities on loan to  broker/dealers  at June 30, 1999,
was  $3,400,000,  for which the fund held cash  collateral of  $3,480,000.  Cash
collateral received is invested in repurchase agreements.

                                       16
<PAGE>
            TRUSTEES AND OFFICERS

JOHN C. BOGLE
Founder, Senior Chairman of the Board, and
Director/Trustee of The Vanguard Group, Inc.,
and each of the investment companies in
The Vanguard Group.

JOHN J. BRENNAN
Chairman of the Board, Chief Executive Officer,
and Director/Trustee of The Vanguard Group, Inc.,
and each of the investment companies in
The Vanguard Group.

JOANN HEFFERNAN HEISEN
Vice President, Chief Information Officer, and a
member of the Executive Committee of Johnson
& Johnson; Director of Johnson & JohnsonoMerck
Consumer Pharmaceuticals Co., Women First
HealthCare, Inc., Recording for the Blind and
Dyslexic, The Medical Center at Princeton, and
Women's Research and Education Institute.

BRUCE K. MACLAURY
President Emeritus of The Brookings Institution;
Director of American Express Bank Ltd., The St.
Paul Companies, Inc., and National Steel Corp.

BURTON G. MALKIEL
Chemical Bank Chairman's Professor of Economics,
Princeton University; Director of Prudential Insurance
Co. of America, Banco Bilbao Gestinova, Baker
Fentress & Co., The Jeffrey Co., and Southern
New England Telecommunications Co.

ALFRED M. RANKIN, JR.
Chairman, President, and Chief Executive Officer
of NACCO Industries, Inc.; Director of NACCO
Industries, The BFGoodrich Co., and The Standard
Products Co.

JOHN C. SAWHILL
President and Chief Executive Officer of The Nature
Conservancy; formerly, Director and Senior Partner of
McKinsey & Co. and President of New York University;
Director of Pacific Gas and Electric Co., Procter &
Gamble Co., NACCO Industries, and Newfield
Exploration Co.

JAMES O. WELCH, JR.
Retired Chairman of Nabisco Brands, Inc.; retired
Vice Chairman and Director of RJR Nabisco; Director
of TECO Energy, Inc., and Kmart Corp.

J. LAWRENCE WILSON
Chairman and Chief Executive Officer of Rohm & Haas
Co.; Director of Cummins Engine Co. and The Mead
Corp.; Trustee of Vanderbilt University.

            OTHER FUND OFFICERS

RAYMOND J. KLAPINSKY
Secretary; Managing Director and Secretary
of The Vanguard Group, Inc.; Secretary of
each of the investment companies in The
Vanguard Group.

THOMAS J. HIGGINS
Treasurer; Principal of The Vanguard Group, Inc.;
Treasurer of each of the investment companies in
The Vanguard Group.

          OTHER VANGUARD OFFICERS

R. GREGORY BARTON
Managing Director, Legal Department.

ROBERT A. DISTEFANO
Managing Director, Information Technology.

JAMES H. GATELY
Managing Director, Individual Investor Group.

KATHLEEN C. GUBANICH
Managing Director, Human Resources.

IAN A. MACKINNON
Managing Director, Fixed Income Group.

F. WILLIAM MCNABB, III
Managing Director, Institutional Investor Group.

MICHAEL S. MILLER
Managing Director, Planning and Development.

RALPH K. PACKARD
Managing Director and Chief Financial Officer.

GEORGE U. SAUTER
Managing Director, Core Management Group.

  "Standard & Poor's(R)," "S&P(R)," "S&P 500(R)," "Standard & Poor's 500," and
  "500" are trademarks of The McGraw-Hill Companies, Inc. Frank Russell Company
   is the owner of trademarks and copyrights relating to the Russell Indexes.
   "Wilshire 4500" and "Wilshire 5000" are trademarks of Wilshire Associates.

<PAGE>

                                    VANGUARD
                                   MILESTONES

                                    [GRAPHIC]
                              The Vanguard Group is
                             named for HMS Vanguard,
                        Admiral Horatio Nelson's flagship
                          at the Battle of the Nile on
                          August 1, 1798. Our founder,
                          John C. Bogle, chose the name
                        after reading Nelson's inspiring
                      tribute to his fleet: "Nothing could
                          withstand the squadron . . .
                       with the judgment of the captains,
                      together with their valour, and that
                        of the officers and men of every
                  description, it was absolutely irresistible."

                                    [GRAPHIC]
                          Walter L. Morgan, founder of
                          Wellington Fund, the nation's
                           oldest balanced mutual fund
                        and forerunner of today's family
                           of some 100 Vanguard funds,
                        celebrated his 100th birthday on
                           July 23, 1998. Mr. Morgan,
                         a true investment pioneer, died
                         six weeks later on September 2.

                                    [GRAPHIC]
                                Wellington Fund,
                        The Vanguard Group's oldest fund,
                         was incorporated by Mr. Morgan
                       70 years ago, on December 28,1928.
                            The fund was named after
                             the Duke of Wellington,
                              whose forces defeated
                            Napoleon Bonaparte at the
                           Battle of Waterloo in 1815.


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[THE VANGUARD GROUP (R) LOGO]

Post Office Box 2600
Valley Forge, Pennsylvania 19482-2600


WORLD WIDE WEB
www.vanguard.com

FUND INFORMATION
1-800-662-7447

INDIVIDUAL ACCOUNT SERVICES
1-800-662-2739

INSTITUTIONAL INVESTOR SERVICES
1-800-523-1036

This report is intended for the fund's
shareholders. It may not be distributed
to prospective investors unless it
is preceded or accompanied by the
current fund prospectus.

Q592-08/11/1999

(C) 1999 The Vanguard Group, Inc.
All rights reserved.
Vanguard Marketing Corporation,
Distributor.


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