In surgical pathology practice, distinguishing malignant from benign melanocytic lesions represents one of the major problem areas. Failure to diagnose a malignant melanoma can have catastrophic results, but separating melanomas from their simulants is often difficult, and over-diagnosis of melanoma is also inappropriate. This fascicle presents a comprehensive account of benign and malignant melanocytic lesions. The benign lesions encompass the major simulants of melanoma. In addition, some of them, such as dysplastic nevi, have significance as markers of individuals at increased risk for the development of melanoma. It has become ever more apparent, especially with the recent advent of molecular classification, that melanoma is not one disease, and that prognosis in melanoma can vary considerably from lesions that present minimal risk, to dangerous malignancies at opposite ends of a spectrum. The details of therapy for these lesions are very different and are determined for the most p