<Page>
- --------------------------------------------------------------------------------
SEC 1815
(11-2002)  Potential persons who are to respond to the collection of information
Previous   contained in this form are not required to respond unless the form
versions   displays a currently valid OMB control number.
obsolete
- --------------------------------------------------------------------------------

                                                           ---------------------
                                                               OMB APPROVAL
                                                           ---------------------
                                                           OMB Number: 3235-0116
                                                           ---------------------
                                                           Expires: August 31,
                                                           2005
                                                           ---------------------
                                                           Estimated average
                                                           burden hours per
                                                           response: 6.00
                                                           ---------------------

                               FORM 6-K
                  SECURITIES AND EXCHANGE COMMISSION
                         WASHINGTON, D.C. 20549

                     REPORT OF FOREIGN PRIVATE ISSUER
                          Dated February 4, 2005

                   PURSUANT TO RULE 13a-16 OR 15d-16
                 OF THE SECURITIES EXCHANGE ACT OF 1934

For the month of February 4, 2005
                ------------------
Commission File Number   001-15244
                      --------------------------------------------

                           CREDIT SUISSE GROUP
- --------------------------------------------------------------------------------
                (Translation of registrant's name into English)

            Paradeplatz 8, P.O. Box 1, CH-8070 Zurich, Switzerland
- --------------------------------------------------------------------------------
                  (Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual
reports under cover Form 20-F or Form 40-F

                       Form 20-F  /X/   Form 40-F  / /
                                -----            -----

Indicate by check mark if the registrant is submitting the Form 6-K in paper as
permitted by Regulation S-T Rule 101(b)(1):
                                           ------

Note: Regulation S-T Rule 101(b)(1) only permits the submission in paper of a
Form 6-K if submitted solely to provide an attached annual report to security
holders.

Indicate by check mark if the registrant is submitting the Form 6-K in paper as
permitted by Regulation S-T Rule 101(b)(7):
                                           ------

Note: Regulation S-T Rule 101(b)(7) only permits the submission in paper of a
Form 6-K if submitted to furnish a report or other document that the registrant
foreign private issuer must furnish and make public under the laws of the
jurisdiction in which the registrant is incorporated, domiciled or legally
organized (the registrant's "home country"), or under the rules of the home
country exchange on which the registrant's securities are traded, as long as the
report or other document is not a press release, is not required to be and has
not been distributed to the registrant's security holders, and, if discussing a
material event, has already been the subject of a Form 6-K submission or other
Commission filing on EDGAR.

Indicate by check mark whether by furnishing the information contained in this
Form, the registrant is also thereby furnishing the information to the
Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

                           Yes  / /   No  /X/
                              -----     -----


If "Yes" is marked, indicate below the file number assigned to the registrant in
connection with Rule 12g3-2(b): 82-
                                   ---------------

<Page>

[CREDIT SUISSE GROUP LETTERHEAD]

                                               Media Relations

                                               CREDIT SUISSE GROUP
                                               P.O. Box 1
                                               CH-8070 Zurich
                                               www.credit-suisse.com


                                               Telephone   +41 1 333 88 44
                                               Telefax     +41 1 333 88 77
                                               media.relations@credit-suisse.com



INCREASE IN THE PROVISION RECORDED BY WINTERTHUR IN CONNECTION WITH THE SALE
OF WINTERTHUR INTERNATIONAL IN THE AMOUNT OF CHF 310 MILLION


Zurich, February 4, 2005 - Credit Suisse Group today announced that its
subsidiary Winterthur Group has recorded a CHF 310 million increase in its
provision (pre-tax) for contingencies relating to the sale of Winterthur
International to XL Insurance (Bermuda) Limited in 2001. Winterthur Group has
undertaken an extensive analysis of recently provided data relating to a
three-year reserve-seasoning exposure, utilizing third-party specialists to
assist in estimating the reserves required for such liabilities. On the basis
of the facts known, Credit Suisse Group believes that the currently recorded
provision is adequate to cover the contingencies related to this transaction.

The amount payable to XL Insurance (Bermuda) Limited is ultimately subject to
an assessment of the Seasoned Net Reserves Amount by an independent actuary,
who will determine which of the estimates submitted by the two parties is
closest to the amount which the independent actuary believes to be the
correct reserve, and that estimate will be conclusively deemed to be the
relevant Seasoned Net Reserves Amount. This process is ongoing and,
consequently, the ultimate resolution of this matter could result in a
further increase in the required provision for the Winterthur International
sale-related contingencies, and any such increase could be significant.

The increase in the provision will be accounted for through the profit and
loss account of Credit Suisse Group and will be reflected in the figures that
it will report for the fourth quarter of 2004 on February 17, 2005.

ENQUIRIES

Credit Suisse Group, Media Relations                  Telephone +41 1 333 88 44

Credit Suisse Group, Investor Relations               Telephone +41 1 333 31 69

Page 1 of 2

<Page>

CREDIT SUISSE GROUP
Credit Suisse Group is a leading global financial services company
headquartered in Zurich. It provides private clients and small and
medium-sized companies with private banking and financial advisory services,
and pension and insurance solutions from Winterthur. In the area of
investment banking, it serves global institutional, corporate, government and
individual clients in its role as a financial intermediary. Credit Suisse
Group's registered shares (CSGN) are listed in Switzerland and in the form of
American Depositary Shares (CSR) in New York. The Group employs around 60,000
staff worldwide. As of September 30, 2004, it reported assets under
management of CHF 1,232.2 billion.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION
This press release contains statements that constitute forward-looking
statements.  In addition, in the future we, and others on our behalf, may
make statements that constitute forward-looking statements.  Such
forward-looking statements may include, without limitation, statements
relating to our plans, objectives or goals; our future economic performance
or prospects; the potential effect on our future performance of certain
contingencies; and assumptions underlying any such statements.  Words such as
"believes," "anticipates," "expects," "intends" and "plans" and similar
expressions are intended to identify forward-looking statements but are not
the exclusive means of identifying such statements.  We do not intend to
update these forward-looking statements except as may be required by
applicable laws.  By their very nature, forward-looking statements involve
inherent risks and uncertainties, both general and specific, and risks exist
that predictions, forecasts, projections and other outcomes described or
implied in forward-looking statements will not be achieved.  We caution you
that a number of important factors could cause results to differ materially
from the plans, objectives, expectations, estimates and intentions expressed
in such forward-looking statements.  These factors include (i) market and
interest rate fluctuations; (ii) the strength of the global economy in
general and the strength of the economies of the countries in which we
conduct our operations in particular; (iii) the ability of counterparties to
meet their obligations to us; (iv) the effects of, and changes in, fiscal,
monetary, trade and tax policies, and currency fluctuations; (v) political
and social developments, including war, civil unrest or terrorist activity;
(vi) the possibility of foreign exchange controls, expropriation,
nationalization or confiscation of assets in countries in which we conduct
our operations; (vii) the ability to maintain sufficient liquidity and access
capital markets; (viii) operational factors such as systems failure, human
error, or the failure to properly implement procedures; (ix) actions taken by
regulators with respect to our business and practices in one or more of the
countries in which we conduct our operations; (x) the effects of changes in
laws, regulations or accounting policies or practices; (xi) competition in
geographic and business areas in which we conduct our operations; (xii) the
ability to retain and recruit qualified personnel; (xiii) the ability to
maintain our reputation and promote our brands; (xiv) the ability to increase
market share and control expenses; (xv) technological changes; (xvi) the
timely development and acceptance of our new products and services and the
perceived overall value of these products and services by users; (xvii)
acquisitions, including the ability to integrate successfully acquired
businesses; (xviii) the adverse resolution of litigation and other
contingencies; and (xix) our success at managing the risks involved in the
foregoing.  We caution you that the foregoing list of important factors is
not exclusive; when evaluating forward-looking statements, you should
carefully consider the foregoing factors and other uncertainties and events,
as well as the risks identified in our most recently filed Form 20-F and
reports on Form 6-K furnished to the US Securities and Exchange Commission.

Page 2 of 2

<Page>

                                 SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, thereunto duly authorized.


                                              CREDIT SUISSE GROUP
                                            -----------------------
                                                   (Registrant)

Date  February 4, 2005                      By:  /s/ David Frick
    ---------------------                       ------------------------------
                                                    (Signature)*
                                                Head of Group Legal & Compliance
*Print the name and title of the signing
officer under his signature.                    /s/ Charles Naylor
                                                    Head of Group Communications