Dysplastic naevi in a population-based survey.

The prevalence of dysplastic naevi was studied in a population-based survey of 380 30 to 39-year-old and 50 to 59-year-old non-Maoris in Milton, a small town in the south of New Zealand. Photographs of all pigmented naevi greater than or equal to 4 mm in diameter were taken during the survey and subsequently evaluated by two experienced reviewers. Nine percent of the group (95% CI, 6%-13%) were judged to have one or more dysplastic naevi. Interobserver agreement over the diagnosis of dysplastic naevi was 85% (kappa = 0.55). Dysplastic naevi were associated with higher counts of moles greater than or equal to 2 mm in diameter; 50 or more such moles increased the likelihood of having three or more dysplastic naevi about 40-fold. Naevi judged to be dysplastic were, therefore, relatively common and were associated with increased numbers of common moles.