A prevalence study of 8298 pupils in compulsory school grades 7--9 was performed in the county of Västerbotten (AC county) in northern Sweden. Prevalence figures for 19 skin diagnoses are presented. A female dominance was found in the prevalence of atopic dermatitis, striae distensae and plantar warts, and a male dominance in multiple pigmented naevi. A sharp drop in atopic dermatitis was found at 13 years. Acne vulgaris showed a negative correlation with atopic dermatitis, ephelides, multiple pigmented naevi and spider naevi and a positive correlation with striae distensae. Atopic dermatitis was negatively correlated to ephelides and multiple pigmented naevi as well as acne. Pronounced variations in the occurrence of plantar warts were registered between different schools. Of the 19 diagnoses registered, only hereditary palmo-plantar keratodermia has a geographical distribution compatible with an increased prevalence of the disease in the AC county. Consequently the figures presented for the other diagnoses are considered to be representative for a north European Caucasian population.