BACKGROUND: The reported frequency of recovery of fungi from infected nails varies according to the geographical area. OBJECTIVES: To establish the nature of the causal agents in a sample of the Libyan population presenting with suspected onychomycosis. METHODS: Samples were taken from the infected fingernails of 648 patients attending the Tripoli Medical Centre. RESULTS: Samples from 500 patients proved positive for fungi following culturing, while 476 were potassium hydroxide and culture positive. Of the culture-positive samples, yeasts of the genus Candida (C. albicans, C. parapsilosis, C. glabrata, C. guillermondii and C. tropicalis) were the dominant cause of this condition in women (417 of 434, 96%) but were responsible for only a minority of cases in men (three of 66, 5%). In contrast, dermatophytes (Trichophyton violaceum, T. rubrum, T. mentagrophytes and Microsporum canis) were responsible for this condition in the majority of cases in men (53 of 66, 80%) but only 3% (15 of 434) of cases in women. The mould Aspergillus nidulans was isolated from the nails of 10 (15%) men and two (0.5%) women. CONCLUSIONS: The data obtained in this study reveal an almost total separation of the aetiological agents responsible for onychomycosis based on gender.