The Spitz nevus has long been defined as a benign melanocytic lesion that shares many histologic features with malignant melanoma. Despite the diagnostic criteria established for these two entities, their histologic similarities continue to make their distinction somewhat difficult. Uncertainties also exist with regard to the natural history of the Spitz nevus; the true pattern of this lesion's biologic behavior remains elusive. As a result, controversies exist with respect to appropriate therapy. To examine these controversies, the epidemiology, clinical features, and histopathology of Spitz nevi, as well as the role of recent molecular and immu-nohistochemical diagnostic studies, are discussed. However, the primary focus of this article is the natural course, prognosis, and treatment of the Spitz nevus. A review of 716 cases of Spitz nevi, compiled from 13 papers published from 1948 to 1990, is presented. After analyzing this and other available data, we propose that at this time Spitz nevi and malignant melanoma cannot easily be categorized as distinct entities and that perhaps they actually exist along one continuum of disease. Because of this uncertainty and the difficulties in differentiating these two lesions, we recommend that treatment include complete excision of all Spitz nevi followed by reexcision of positive margins if present.