Pseudallescheria boydii is a recognized cause of mycetoma, a chronic fungal disease that usually affects the extremities. Isolated case reports have also implicated P. boydii in infections of other sites. We report the first large series (83 isolates) of P. boydii in 46 patients, including the second report of P. boydii brain abscess and disseminated infection in a noncompromised host. Between 1974 and 1984 at our institution, P. boydii was cultured from a variety of sites: respiratory tract, 36; soft tissue, 25; bone, 9; gastric aspirate, 4; maxillary sinus, 2; wound, 2; urine, 2; brain abscess, 1; ear, 1; and toenail, 1. Pulmonary colonization proved to be the most common form of pseudallescheriasis of the lung (34 of 36 cultures in this category); 28 of the 32 patients with pulmonary infections had received immunosuppressive therapy or had an underlying disorder. The importance of isolation of P. boydii from bone and soft tissue is supported in this series because all 9 cultures from bone and 21 of 25 cultures from soft tissue were associated with infection. Of 10 cases of infection, 5 were osteomyelitis and 2 were infected wounds; in addition, maxillary sinusitis, disseminated infection, and a lung abscess occurred in 1 patient each.