Onychomycoses, infections of the nail caused by fungi, are amongst the most common illnesses. Because of the high incidence of these infections and problems involved in their therapy, they have received much attention, particularly as concerns a better characterisation of the causative micro-organisms. Onychomycosis caused by dermatophytes (tinea unguium) is most common and is found more frequently on the feet than on the hands. The clinical presentation of onychomycosis is at best indicative of fungal infection, and the growth of a credible pathogen is an indispensable prerequisite for definite diagnosis. The clinical appearance is variable. Four major types of manifestation have been characterised, depending on localisation and spread. New antifungal agents for systemic or topical application based on novel active substances or vehicles are available, and cure is feasible for the majority of cases. Therapy can and should be individualised, depending on the characteristics of the particular case. Currently, continuous or intermittent oral treatment with itraconazole or terbinafine exhibit a particularly favourable risk : benefit ratio. Fluconazole might become an alternative in the near future. With respect to topical treatment, ciclopirox or amorolfine lacquer and the bifonazole/urea combination deserve particular interest. However, cure cannot be expected for every case.