Malignant melanoma is a more heterogeneous neoplasm than indicated by the four histologic types described by Clark and his associates. In this study, we focused attention on the histologic morphology of malignant melanocytes in nodules of malignant melanoma and have identified at least four additional subtypes. Determination of "nodule type" appears to be superior to the Breslow measurement of thickness in predicting metastases and death. Based on our experience with this study, we believe that a review of the microscopic slides from a larger series of cases, with at least eight years follow-up, may reveal other "nodule types" and may also further divide these four subtypes into yet more groups.