Onychomycosis is the most frequently encountered nail disease and may be difficult to diagnose and treat. The objective of this study was to determine the prevalence, the clinical and mycological characteristics of onychomycosis in central Tunisia. It is a retrospective study performed over a 22-year period (1986–2007). It included 7151 patients (4709 women and 2442 men) with suspected fingernails and/or toenails onychomycosis. The patients were referred to the Mycology-Parasitology Laboratory of Farhat Hached hospital in Sousse for mycological examination. Both direct microscopy and culture of the nail material were performed to diagnose and identify the causative fungal species. Onychomycosis was confirmed in 78.6% of investigated patients (5624/7151). The positivity rate was higher in women as compared with men. In both men and women, fingernails were most frequently involved than toenails. No significant relation was found between gender and toenails onychomycosis, whereas fingernails were frequently involved in women. As far as aetiological agents are considered, dermatophytes, yeast and moulds were responsible for 49.9%, 47.4% and 2.7% of onyxis cases respectively. In fingernail infections, yeast were the most frequent fungi (83.6%), Candida albicans being the leading species (51.6%). In contrast, in toenail infections, dermatophytes were more frequent (74.1%). Trichophyton rubrum was by far the dominant species (88.1%). Yeast were observed more frequently in women whereas dermatophytes were more common in men. Moulds were involved in 4.2% of cases. The most frequent species were Aspergillus sp. and Chrysosporium sp. Onychomycosis is a frequent disease in central Tunisia. T. rubrum is the predominant agent in toenails infection and yeast, mainly C. albicans, in fingernails onychomycosis.