1
                                                                     Exhibit 8.1

                    [STIBBE SIMONT MONAHAN DUBOT LETTERHEAD]

                                             3 July 2000

Ladies and Gentlemen:

We are acting as Belgian counsel to deCODE genetics, Inc. ("deCODE") in
connection with the Registration Statement on Form S-1 (the "Registration
Statement") filed with the United States Securities and Exchange Commission by
deCODE for the purpose of registering deCODE's common stock under the United
States Securities Act 1933 (the "Securities Act") in connection with the
proposed initial public offering and listing of deCODE's common stock on the
Nasdaq National Market and EASDAQ. We have examined such matters of fact and law
as we have deemed necessary or advisable for the purpose of this opinion. The
present opinion is confined to and given on the basis of Belgian law as it
exists at the date hereof. We have more in particular made no investigation on
the laws of any other jurisdictions referred to in the Registration Statement as
a basis for this opinion and we do not express or imply any opinion thereon.
There is no intention on our part to amend or update this opinion in the event
of any changes after the date hereof in any Belgian laws or regulations relevant
to this opinion.

Based on the foregoing, we are of the opinion that the statements in the
prospectus contained in the Registration Statement (the "Prospectus") under the
caption "Certain Tax Considerations -- Certain Belgian Tax Considerations for
Belgian Holders of Common Stock", insofar as such statements relate to the
Belgian income and stamp tax consequences currently applicable to the Belgian
holders discussed therein, fairly describe the material tax consequences of the
proposed initial public offering.
   2


Stibbe Simont Monahan Duhot

We are members of the Dutch Speaking Brussels Bar Association and are as such
qualified to practice law in Belgium.


We hereby consent to the use of our name under the caption "Certain Tax
Considerations -- Certain Belgian Tax Considerations for Belgian Holders of
Common Stock" in the Prospectus and to the filing, as an exhibit to the
Registration Statement, of this opinion. In giving such consent, we do not admit
that we come within the category of persons whose consent is required under
Section 7 of the Securities Act.


The present opinion shall be governed by and construed in accordance with
Belgian law as in effect on the date at which it is given and any matters
relating to it shall be of the exclusive jurisdiction of the Belgian courts.

Yours faithfully,



/s/ Jan Peeters                              /s/ Luc De Broe
-----------------                            -------------------
    Jan Peeters                                  Luc De Broe





                                      -2-