We present a case of fungal endocarditis in a 42-year-old man with a history of intravenous drug abuse who required aortic valve replacement for severe aortic insufficiency. Cultures of the resected valve grew Pseudallescheria boydii. The patient subsequently developed persistent endocarditis of the prosthetic valve with systemic embolism. At autopsy, cultures of the prosthetic valve grew Monosporium apiospermum, an anamorph of Pseudallescheria boydii. Although fungal endocarditis is not uncommon in intravenous drug abusers, endocarditis caused by Pseudallescheria boydii is rare. It has been reported in only three other instances, and under circumstances that were different from ours.