Exhibit 5.1
                                McGuireWoods LLP
                         9 West 57th Street, Suite 1620
                          New York, New York 10019-2602



December 2, 2003



Board of Directors
Diomed Holdings, Inc.
One Dundee Park
Andover, MA 01810

Ladies and Gentlemen:

         We are acting as counsel to Diomed Holdings, Inc., a Delaware
corporation (the "Company"), in connection with the filing with the Securities
and Exchange Commission (the "Commission"), under the Securities Act of 1933, as
amended (the "Act"), of the Registration Statement on Form SB-2 (the
"Registration Statement") relating to the offer and sale pursuant to the
Registration Statement, by the Selling Stockholders identified in the
Registration Statement, of up to 327,569,867 shares of common stock, par value
$0.01 per share, of the Company (the "Shares"). This opinion letter is furnished
to you for filing with the Commission pursuant to Item 601 of Regulation S-K
promulgated under the Act.

         In  reaching  the  opinion  stated  in this  letter,  we have  reviewed
originals  of  copies  of  the  Registration   Statement,   the  Certificate  of
Incorporation  and the Bylaws of the Company,  both as amended to date, and such
other  documents as we have  considered  relevant.  We have assumed that (i) all
information  contained  in all  documents  reviewed by us is  correct,  (ii) all
signatures  on all  documents  reviewed by us are genuine,  (iii) all  documents
submitted to us as originals are true and complete, (iv) all documents submitted
to us as copies are true and complete copies of the originals thereof,  (v) each
natural person signing any document  reviewed by us had the legal capacity to do
so and (vi)  each  natural  person  signing  in a  representative  capacity  any
document reviewed by us had authority to sign in such capacity.

         Based upon the  foregoing,  it is our opinion  that the Shares are duly
authorized, validly issued, fully paid and nonassessable.

         The opinion  expressed above is limited to matters governed by the laws
of the State of  Delaware.  We  express no  opinion  herein  about the effect of
federal or state securities laws or the laws of any other jurisdiction.

         We hereby  consent to the use of this opinion  letter as Exhibit 5.1 to
the  Registration  Statement and to the use of our name under the heading "Legal
Matters"  therein.  In giving this  consent,  we do not admit that we are in the
category of persons whose consent is required  under Section 7 of the Act or the
rules and regulations of the Commission promulgated thereunder.

         This opinion letter speaks as of the date hereof.  We disclaim any duty
to advise you  regarding  any  change  subsequent  to the date  hereof in, or to
otherwise communicate with you with respect to, the matters addressed herein.

                                            Very truly yours,

                                            McGuireWoods, LLP