Two hundred forty-eight cases of melanoma accessioned from 1984 through 1985 were independently reviewed by a panel of dermatopathologists for the presence of nevomelanocytic proliferations in histologic contiguity with melanoma. One hundred ninety-seven cases remained in the sample for analysis after cases with insufficient histologic material and those diagnosed without primary melanoma were excluded. We found that 32.5% of melanomas (95% confidence interval, 25.9% to 39.7%) were associated with a benign or dysplastic nevus in histologic contiguity. Melanoma type and anatomic location were significant predictors of contiguous nevomelanocytic proliferations when considered alone. After adjustment, however, only melanoma type significantly predicted the presence of a contiguous nevus. Superficial spreading melanomas were approximately 11 times more likely to contain histologic evidence of a precursor nevus than was nodular melanoma (odds ratio, 11.1; 95% confidence interval, 1.4 to 86.6) and were almost 22 times more likely to be associated with a nevus than was lentigo maligna melanoma (odds ratio, 21.45; 95% confidence interval, 2.8 to 162.4). This evidence supports the concept of the heterogeneity of melanoma histogenesis.