The aim of this study was to determine the prevalence of longitudinal melanonychia (ML) in white subjects in order to obtain epidemiological data suggesting management strategies. We included 99 hospitalized patients in this study, all were examined by a dermatologist. Another 4,400 healthy subjects were examined by a general practitioner. Criteria retained were age, sex, the presence or not of ML, the localization, number of bands, intensity of the coloration and size. The prevalence of ML was 12.6 +/- 3.4 p. 100 (CI 5.9-19.3) and 1.4 +/- 0.18 p. 100 (CI 1.3-1.75) respectively in the 99 and 4,400 subjects. The percentage of subjects increased progressively with age, particularly after 45 years and reached a peak between 56 and 65 years. The age distribution was identical. The most frequent localization was the thumb, followed by the great toe and the index. None of the ML observed had a clinical presentation suggestive of melanoma and no biopsies were taken. The frequency of melanonychia is thus higher in this series than that reported by previous studies where less than 1 p. 100 of the subjects had melanonychia. It was highest between the ages of 45 and 65 years. These results should be used when counselling patients and proposing systematic exeresis of ML above the age of 45 years.