A small subset of patients with thin (less than 0.76 mm thick) primary cutaneous malignant melanomas develop metastases. Features that may help differentiate higher and lower risk lesions in this thickness range are reported to include the patient's age and sex, anatomic site and diameter of the primary lesion, Clark level of invasion, development of a vertical growth phase, the mitotic index, ulceration, regression, and cellular aneuploidy. In this report, we review the literature regarding the significance of these factors on the patient's prognosis.