<PAGE>
Prospectus Supplement filed under Rule 424(b)(3)
in connection with Registration Statement No. 333-48047
PROSPECTUS SUPPLEMENT NO. 4 DATED DECEMBER 16, 1998
(To Prospectus Dated May 28, 1998)
PLATINUM technology, inc.
$150,000,000 6.25% CONVERTIBLE SUBORDINATED NOTES DUE 2002
AND SHARES OF COMMON STOCK ISSUABLE UPON CONVERSION THEREOF
This Prospectus Supplement No. 4 ("Fourth Prospectus Supplement") supplements
the information contained in PLATINUM technology, inc.'s Prospectus dated May
28, 1998 (the "Prospectus") as supplemented by Prospectus Supplement No. 1 dated
July 13, 1998, Prospectus Supplement No. 2 dated August 31, 1998 and Prospectus
Supplement No. 3 dated September 18, 1998, relating to the offer and sale by the
Selling Securityholders of up to $150,000,000 in principal amount of PLATINUM
technology, inc.'s 6.25% Convertible Subordinated Notes Due 2002 and shares of
Common Stock issuable if these notes are converted. This Fourth Prospectus
Supplement is not complete without, and may not be delivered or used except in
connection with, the Prospectus, Prospectus Supplement No. 1, Prospectus
Supplement No. 2 and Prospectus Supplement No. 3 including any amendments or
supplements thereto. Capitalized terms used herein but not defined have the
meanings assigned to such terms in the Prospectus. The following table amends
and supplements the information set forth in the Prospectus under the caption
"Selling Securityholders."
<TABLE>
<CAPTION>
Principal Amount of
Securities Beneficially Owned
-----------------------------------
Number of
Shares of
Number of Principal Common
Principal Shares of Amount of Stock
Amount of Common Notes That That May
Name Notes Percentage Stock(1)(2) May Be Sold Be Sold
- --------------------------------- ---------- ---------- ----------- ----------- ------------
<S> <C>
Sage Capital $ 1,500,000 1.0% 41,605 $ 1,500,000 41,605
TQA Leverage Fund, L.P. 3,000,000 2.0 83,211 3,000,000 83,211
Any other holders of Notes(3)(4) 14,795,000 9.7 410,373 14,795,000 410,373
</TABLE>
__________________
* Less than 1%.
(1) Assumes conversion of the full amount of Notes held by such holder at the
initial rate of $36.0525 in principal amount of Notes per share of Common
Stock; such conversion price is subject to adjustment as described in the
Prospectus under "Description of Notes - Conversion." Under the terms of
the Indenture, fractional shares will not be issued upon conversion of the
Notes; cash will be paid in lieu of any fractional shares.
(2) The number of conversion shares beneficially owned by each Selling
Securityholder named herein is less than 1% of the Company's outstanding
Common Stock as of December 16, 1998.
(3) Information concerning other Selling Securityholders will be set forth in
supplements to this Prospectus from time to time, if required.
(4) Assumes that "Any other holders of Notes" do not beneficially own any Common
Stock other than the Common Stock issuable upon conversion of the Notes at
the initial conversion price.
This Prospectus Supplement is dated December 16, 1998
