The study analysed the relationship between high counts of common naevi and numbers of atypical naevi (AN) in sites differing in exposure to the sun. A series of 90 subjects with 100 or more common naevi (cases) and 92 controls was investigated by means of a case-control study. A striking association between high numbers of common naevi and prevalence of AN (whole body) was found. The adjustment for phenotype and phototype did not obscure this association. Similar findings were obtained after exclusion of subjects with familiarity for melanoma. Cases had more AN than controls in all the body sites, except for the buttocks, where sun exposure can be considered minimal or absent: in this site, an excess of common naevi but not of AN was found. The present study suggests that subjects with high common naevi counts show a higher prevalence of AN independently of their complexion, sunburn history and family history of melanoma. Phenotypic expression of AN seems to be enhanced by direct sun exposure.