The diagnosis of malignant melanoma is based on clinical grounds and a properly performed biopsy, preferably excision, so that the type of melanoma and the thickness can be assessed by methods described by Clark and Breslow. These facilitate clinical and pathologic staging. Excisions with conservative margins for thin lesions (less than 1.0 mm in thickness) and more extensive margins for thicker lesions are appropriate. The issue of elective lymph node dissection is controversial. Most authors agree it is not indicated for lesions less than 1.0 mm thick and may offer little advantage for lesions greater than 4.0 mm thick. Several retrospective studies show a survival advantage in patients with "intermediate" thickness melanomas who may have occult nodal metastases. However, there are prospective randomized clinical trials supporting the concept that positive lymph nodes are a manifestations of systemic disease, and survival is equivalent in patients who have subsequent therapeutic lymph node dissections. A procedure using intraoperative lymphatic mapping and selective lymphadenectomy may identify those patients who are likely to benefit from lymphadenectomy.