Scedosporium prolificans, a mold morphologically similar to Scedosporium apiospermum, may cause asymptomatic colonization or localized or disseminated infection following trauma, surgery, and immunosuppression. S. prolificans is normally resistant to available antifungal agents, and prognosis depends largely on the host's immune status, extent of infection, and feasibility of surgical debridement. We report on 16 patients with deep S. prolificans infections, focusing on predisposing factors, clinical characteristics, outcome, postmortem findings, and antifungal susceptibility testing to 6 antifungal agents. Between 1989 and 1994, 16 cases of deep infections by S. prolificans were documented in 6 clinical centers in Spain (15 adults and 1 child: male/female = 0.77). Fifteen patients had underlying hematologic malignancy (14 with neutropenia) and 1 had a prosthetic cardiac valve. Syndromes included disseminated infection in 14 patients (1 with prosthetic valve endocarditis) and fungal pneumonia and meningoencephalitis in 1 patient each. S. prolificans was isolated from 2 specimens in 14 patients and from 1 specimen in 2 patients (blood, n = 12; respiratory tract, n = 4; CNS, n = 4; and skin biopsy, n = 3). Antifungal susceptibility testing by a micromethod with RPMI-2% glucose medium was performed in 8 isolates, all of which were resistant to amphotericin B, flucytosine, ketoconazole, fluconazole, itraconazole, and miconazole. All patients received antifungal therapy (amphotericin B, n = 9; amphotericin B+ flucytosine, n = 1; amphotericin B+ itraconazole, n = 2; liposomal amphotericin B+ itraconazole, n = 1; amphotericin B+ fluconazole, n = 1 and 2 underwent surgical procedures. Two patients survived coinciding with hematologic recovery and 14 (87.5%) patients died in a median time of 4 days after the first positive culture (range, 0-60 d). Necropsy was performed in 10 patients, and disseminated infection was found in 9. In conclusion, S. prolificans is an emerging multiresistant fungal pathogen that may cause asymptomatic colonization, localized infection related to trauma or surgery, and rapidly fatal disseminated infection in immunocompromised hosts, particularly those with neutropenia. This mycosis underscores the urgent need for new antifungal agents.