Clinical photographs of 79 prospectively studied cases of non-familial cutaneous malignant melanoma were reviewed; special attention was directed to the distribution pattern of coexistent melanocytic lesions. A group of 15 patients had moles on the covered buttock area. Seven of these patients had large clinically atypical nevi, and biopsies of these nevi showed severe melanocytic dysplasia. Residual elements of melanocytic dysplasia were identified in five of the primary melanomas in this group of patients. It is suggested that these patients represent a distinctive syndrome, the Dysplastic Nevus Syndrome (DNS) and that they are at increased risk for development of primary cutaneous malignant melanoma. The clinically and histologically distinctive dysplastic nevi of these patients are identical to the precursor lesion for melanoma that we have previously described in a familial context, the B-K mole syndrome. This paper represents the first description of this form of dysplasia in non-familial melanoma.