Tinea unguium is a common, chronic fungal infection of the nails. Many epidemiological studies have looked at the frequency with which this condition is seen in hospital outpatients clinics or mycological laboratories along with other dermatomycoses. Only recently have studies begun to emerge looking at the prevalence of this condition in populations. Hospital and mycological laboratory-based studies give valuable information about tinea unguium prevalence in a particular clinic, but cannot be compared with other studies due to confounding factors inherent in the different people attending individual clinics. From population-based studies the prevalence of tinea unguium lies between 2 and 8%. Tinea unguium increases steadily with age. It is infrequent but definitely found in children. With the increasing life expectancy in the Western world the prevalence of tinea unguium is likely to increase further without adequate prevention and treatment.