A completely revised staging system for cutaneous melanoma was implemented in 2003. The changes were validated with a prognostic factors analysis involving 17,600 melanoma patients from prospective databases. This major collaborative study of predicting melanoma outcome was conducted specifically for this project, and the results were used to finalize the criteria for this evidence-based staging system. In fact, this was the largest prognostic factors analysis of prospectively followed melanoma patients ever conducted. Important results that shaped the staging criteria involved both the tumor-node-metastasis (TNM) criteria and stage grouping for all four stages of melanoma. Major changes in the staging include: (1) melanoma thickness and ulceration are the dominant predictors of survival in patients with localized melanoma (Stages I and II); deeper level of invasion (ie, IV and V) was independently associated with reduced survival only in patients with thin or T1 melanomas. (2) The number of metastatic lymph nodes and the tumor burden were the most dominant predictors of survival in patients with Stage III melanoma; patients with metastatic nodes detected by palpation had a shorter survival compared with patients whose nodal metastases were first detected by sentinel node excision of clinically occult or “microscopic” metastases. (3) The site of distant metastases (nonvisceral versus lung versus all other visceral metastatic sites) and the presence of elevated serum lactate dehydrogenase (LDH) were the dominant predictors of outcome in patients with Stage IV or distant metastases. (4) An upstaging was implemented for all patients with Stage I, II, and III disease when a primary melanoma is ulcerated by histopathological criteria. (5) Satellite metastases around a primary melanoma and in-transit metastases were merged into a single staging entity that is grouped into Stage III disease. (6) A new convention was implemented for defining clinical and pathological staging so as to take into account the new staging information gained from lymphatic mapping and sentinel node biopsy.