The purpose of this study was to determine the prevalence of causative non-dermatophytic filamentous fungi in onychomycosis in Izmir, Turkey, July 2001-December 2002. Totally 83 0 samples of nail scrapings from 716 patients with presumptive onychomycosis were prospectively studied, making consecutive cultures from each patient 3 times, with a-week interval in between, using conventional mycological methods. Molds were detected in 25 (12%), yeasts in 97 (47%) and dermatophytes in 84 (41%). The molds, in order of frequency, were Aspergillus niger (7), Fusarium spp. (6), Ulocladium spp. (4), Acremonium spp. (2), sterile mycelia (2), Alternaria sp. (1), Aspergillus flavus (1), Cladosporium sp. (1), and Scopulariopsis sp. (1). Careful evaluation of "molds" in onychomycosis is very important for its implications in the management of the disease.