Cutaneous melanoma may occur as isolated, so-called 'sporadic' cases or in association with multiple atypical naevi and in familial clusters, in which case it is referred to as the familial dysplastic naevus syndrome (DNS). In this retrospective study (a) the number and body distribution of naevocytic naevi and (b) the body distribution of malignant melanoma (MM) in individuals with familial DNS were compared in order to study their association. In 45 patients with familial DNS aged 20-39 years naevus counts on trunk and lower extremities were compared with melanoma data and distributions from a second group of 43 patients from the same DNS families aged 12-66 years. Men had significantly more naevi of a size > or = 2 mm or > or = 5 mm on the back than women (P = 0.02). Women showed a tendency towards a greater number of naevi on the lower extremities than men, but in women no significant difference in naevi between the lower extremities and the back was found. The total number of naevi on the trunk and lower extremities in familial DNS patients was higher than that in the general population. In conclusion, it was found that predilection sites for melanoma in familial DNS patients of both sexes correspond with the distribution of naevi; in males naevi and melanoma counts and percentage distributions were higher on the back, in females both the back and the lower extremities were affected. These findings strongly suggest an association between naevus distribution and melanoma occurrence and site in familial DNS, analogous to earlier reports on sporadic melanoma.