Infection due to Fusarium species is an increasing cause of serious potentially fatal disease in patients with cancer. We described 9 patients with infection caused by Fusarium species during a 4-year period at the M. D. Anderson Hospital. The spectrum of infections included disseminated disease in 4 patients, skin or soft-tissue infections in 3, pneumonia in 1, and fungemia in 1. All 4 patients with disseminated infection had culture- and biopsy-proven skin lesions caused by Fusarium species and the blood cultures yielded the organism in 3 of these 4 patients. Maxillary sinusitis was the presenting manifestation of Fusarium infection in 2 of these 4 patients, suggesting that paranasal sinuses are potential portals of entry for the infection. Eight patients had a hematological malignancy and 7 were neutropenic at the onset of their infection. Patients with deep-seated infections remained neutropenic and died from infection despite treatment with amphotericin B. All 5 isolates tested in vitro showed resistance to ketoconazole and miconazole, whereas 3 were susceptible to amphotericin B. Fusarium species could play a role in producing myelosuppression and fungal cultures are required to differentiate it from the more commonly encountered Aspergillus species. Fusarium species are emerging as a serious, potentially fatal, pathogen in patients with cancer.