The melanoma risk associated with dysplastic nevi outside the context of familial melanoma was studied by the case-control method. One hundred five newly diagnosed incident melanoma cases with negative family histories for familial melanoma and 181 controls (frequency matched for race, age, and sex) were studied by personal interview and cutaneous examination. The prevalence of dysplastic nevi was 41 (39%) of 105 in the cases and 13 (7%) of 181 in the controls. The odds ratio for dysplastic nevi by multiple logistic regression analysis simultaneously correcting for age, sex, eye color, hair color, actinic damage, freckles, and total number of nondysplastic nevi was 6.8 (95% confidence interval, 2.7, 16.9). This study supports the significance of dysplastic nevi as markers of increased risk for nonfamilial melanoma.