Aspergillosis typically occurs in patients with reduced host defenses; such patients include renal and marrow recipients as well as patients with chemotherapy-induced myelosuppression. Pulmonary structures are most frequently involved; non-pulmonary involvement (including sinus) has not been frequently reported. In the present study, paranasal sinusitis occurred in 52 myelosuppressed cancer patients treated over 5 years at the UMCC with chemotherapy. Twenty-one patients had Aspergillus sinusitis; Aspergillus spp., including flavus and niger, were directly recovered from sinus in 19 of the 21 infections. Two other patients were considered clinically, although not microbiologically, documented. Multiple predisposing factors for Aspergillus sinusitis during the 60 days prior to infection diagnosis appear to exist; these include: 1) granulocyte count less than 500 mm3 (mean duration, 42 days versus 14 days for sinusitis of other etiology; P less than 0.001); 2) prolonged hospitalization (mean duration, 22 days versus 14 days for patients with non-fungal sinusitis; P less than 0.001); and 3) prolonged antibiotic therapy (mean duration, 22 days versus 9 days; P less than 0.001). The Aspergillus sinusitis resolved in 18 of 21 patients following treatment with amphotericin B; however, 11 of 18 patients had infection recurrence that always developed when tumor recurred and chemotherapy was reinstituted.