To revise the staging system for cutaneous melanoma under the auspices of the American Joint Committee on Cancer (AJCC). The prognostic factors analysis described in the companion publication (this issue), as well as evidence from the published literature, was used to assemble the tumor-node-metastasis criteria and stage grouping for the melanoma staging system. Major changes include (1) melanoma thickness and ulceration but not level of invasion to be used in the T category (except for T1 melanomas);(2) the number of metastatic lymph nodes rather than their gross dimensions and the delineation of clinically occult (ie, microscopic) versus clinically apparent (ie, macroscopic) nodal metastases to be used in the N category;(3) the site of distant metastases and the presence of elevated serum lactic dehydrogenase to be used in the M category;(4) an upstaging of all patients with stage I, II, and III disease when a primary melanoma is ulcerated;(5) a merging of satellite metastases around a primary melanoma and in-transit metastases into a single staging entity that is grouped into stage III disease; and (6) a new convention for defining clinical and pathologic staging so as to take into account the staging information gained from intraoperative lymphatic mapping and sentinel node biopsy. This revision will become official with publication of the sixth edition of the AJCC Cancer Staging Manual in the year 2002. J Clin Oncol 19: 3635-3648.© 2001 by American Society of Clinical Oncology.