<PAGE>
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
Form 13F
FORM 13F COVER PAGE
Report for the Calendar Year or Quarter Ended: December 31, 1999
Check here if Amendment //; Amendment Number:
This Amendment (Check only one.): // is a restatement.
// adds new holdings entries.
Institutional Investment Manager Filing this Report:
Name: Chesapeake Partners Management Co., Inc.
Address: 1829 Reisterstown Road
Suite 220
Baltimore, Maryland 21208
Form 13F File Number: 28-4120
The institutional investment manager filing this report and the person by whom
it is signed hereby represent that the person signing the report is authorized
to submit it, that all information contained herein is true, correct and
complete, and that it is understood that all required items, statements,
schedules, lists, and tables, are considered integral parts of this form.
Person Signing this Report on Behalf of Reporting Manager:
Name: Mark D. Lerner
Title: Vice President
Phone: (410) 602-0195
Signature, Place, and Date of Signing:
/s/ Mark D. Lerner Baltimore, Maryland 2/14/00
--------------------------- ------------------- ----------------------
[Signature] [City, State] [Date]
Report Type (Check only one.):
/X/ 13F HOLDINGS REPORT. (Check here if all holdings of this reporting manager
are reported in this report.)
// 13F NOTICE. (Check here if no holdings reported are in this report, and
all holdings are reported by other reporting manager(s).)
// 13F COMBINATION REPORT. (Check here if a portion of the holdings for this
reporting manager are reported in this report and a portion are reported
by other reporting manager(s).)
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FORM 13F SUMMARY PAGE
Report Summary:
Number of Other Included Managers: 0
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Form 13F Information Table Entry Total: 43
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Form 13F Information Table Value Total: $480,182
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(thousands)
List of Other Included Managers:
Provide a numbered list of name(s) and Form 13F file number(s) of all
institutional investment managers with respect to which this report is filed,
other than the manager filing this report.
[If there are no entries in this list, state "NONE" and omit the column headings
and list entries.]
None
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FORM 13F INFORMATION TABLE
<TABLE>
<CAPTION>
COLUMN 1 COLUMN 2 COLUMN 3 COLUMN 4 COLUMN 5 COLUMN 6 COLUMN 7 COLUMN 8
- --------------------- ---------------- -------- -------- ------------------------- ---------- -------- ----------------
VALUE SHRS OR SH/ PUT/ INVESTMENT OTHER VOTING
NAME OF ISSUER TITLE OF CLASS CUSIP (x$1000) PRN AMT PRN CALL DISCRETION MANAGERS AUTHORITY
- --------------------- ---------------- -------- -------- ---------- ---- ----- ---------- -------- ----------------
SOLE SHARED NONE
---- ----- ----
<S> <C> <C> <C> <C> <C> <C> <C> <C> <C> <C> <C>
Adforce, Inc. Common 006867105 4,996 70,000 SH sole sole
- -----------------------------------------------------------------------------------------------------------------------------------
AHT Corporation Common 00756H108 2,078 443,300 SH sole sole
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Air Express Int'l Common 009104100 323 10,000 SH sole sole
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Amcol International Common 02341W103 285 17,700 SH sole sole
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Abbott Laboratories Common 002824100 15,658 431,190 SH sole sole
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Allied Signal Common 438516106 1,579 27,375 SH sole sole
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Caremark, Inc. Common 58503X107 32,403 6,400,500 SH sole sole
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Catherines Stores Common 14916F100 735 35,000 SH sole sole
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Computer Sciences Common 205363104 3,823 40,400 SH sole sole
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Diamond Fields Intl Common 252905104 402 341,800 SH sole sole
- -----------------------------------------------------------------------------------------------------------------------------------
Dynatech New Common 268140100 2,117 313,600 SH sole sole
- -----------------------------------------------------------------------------------------------------------------------------------
Doubleclick, Inc. Common 258609304 37,403 147,800 SH sole sole
- -----------------------------------------------------------------------------------------------------------------------------------
Exxon Mobile Corp. Common 30231G102 3,480 43,200 SH sole sole
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Fleet Fin. Warrants Common 338915119 2,001 68,992 SH sole sole
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Flycast Comm. Common 344067103 8,173 62,900 SH sole sole
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General Dynamics Common 369550108 3,566 67,600 SH sole sole
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General Instruments Common 370120107 96,807 1,138,900 SH sole sole
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Genesys
Telecom Labs Common 371931106 10,680 197,200 SH sole sole
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Healthsouth Corp. Common 421924101 940 174,800 SH sole sole
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Imasco Ltd. Common 452451701 22,481 813,200 SH sole sole
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IPC Communications Common 44980K206 23,281 327,900 SH sole sole
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Illinois Toolworks Common 452308109 16,933 250,633 SH sole sole
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Infinity Broadcasting Common 456625102 30,936 854,875 SH sole sole
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Mattel, Inc. Common 577081102 1,146 87,280 SH sole sole
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Medimmune, Inc. Common 584699102 4,324 26,070 SH sole sole
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Nfront, Inc. Common 65334N109 200 10,000 SH sole sole
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Oak Industries Common 671400505 15,144 142,700 SH sole sole
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Ontrack Data Intl Common 683372106 844 70,000 SH sole sole
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Optical Coating Lab Common 683829105 48,426 163,600 SH sole sole
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Pittway Corp Cl A Common 725790208 5,996 133,800 SH sole sole
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Sybron Chemicals Common 870903101 1,159 98,600 SH sole sole
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Scottish Power Common 81013T705 1,260 45,000 SH sole sole
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Shire Pharmaceuticals Common 82481R106 3,044 105,205 SH sole sole
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Solectron Corp. Common 834182107 6,212 65,300 SH sole sole
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Thermadyne Holdings Common 883435208 507 26,004 SH sole sole
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Tyco International Common 902120104 8,198 210,200 SH sole sole
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United Globalcom Common 910734102 7,741 109,600 SH sole sole
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US Bancorp Common 902973106 1,238 52,000 SH Call sole none
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UST Corp. Common 902900109 12,398 390,500 SH sole sole
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Ventiv Health Common 922793104 4,556 495,932 SH sole sole
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Visio Corporation Common 927914101 33,459 704,400 SH sole sole
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Visio Corporation Common 927914101 2,138 45,000 SH Put sole none
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Watkins Johnson Common 942486101 1,112 27,800 SH sole sole
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</TABLE>
