[A woman with thick nails and a white tongue].

A 22-year-old women visited the dermatologist with hypertrophic finger- and toenails, palmoplantar keratoderma and oral leukokeratosis since her childhood. The diagnosis 'pachyonychia congenita type 1' was made. This is a rare dermatosis with an autosomal dominant inheritance pattern. The treatment is symptomatic.