Among the various clinical and histologic criteria used to differentiate between benign and malignant melanocytic neoplasms, emphasis has been placed on the size of the lesion. Malignant melanomas, when diagnosed, are usually larger than 6 mm in diameter whereas most acquired melanocytic nevi tend to be smaller. We tested this size criterion with a retrospective clinicopathologic study of 30 proliferations of atypical melanocytes within the epidermis and dermis that measured less than 6 mm in diameter. Nineteen cases fulfilled all 15 established histologic criteria for the diagnosis of malignant melanoma. The remaining 11 cases fulfilled 14 of 15 criteria. Four of eight of these small malignant melanomas analyzed by multiparameter flow cytometry were aneuploid (DNA ploidy index less than or equal to 0.9 or greater than or equal to 1.1). The sex ratio, race, and anatomic sites associated with these small melanomas were similar to those described in patients with malignant melanomas larger than 6 mm in diameter. Furthermore, one melanoma metastasized to a regional lymph node and another recurred. We conclude that small malignant melanomas less than 6 mm in diameter can have histologic features, DNA abnormalities, clinical presentations, and biologic potentials similar to larger lesions.