During the past few decades, scientific data relating to melanoma have flourished. New information regarding acquired nevi, dysplastic nevi (atypical nevi), and congenital nevi has given us a better understanding of these precursor lesions and their relationships to malignant melanoma. The roles of laboratory testing, photography, and newer diagnostic tools (eg, epiluminescence) to evaluate patients for melanoma or precursor lesions have fallen under close scrutiny. Traditional surgical therapeutic interventions continue to be replaced by less aggressive protocols based on prospective randomized studies. Many new interventions such as sentinel lymph node procedures are currently being evaluated at research/referral centers around the world. We present clinicians with an evidence-based summary of the current literature with regard to primary cutaneous melanoma, its diagnosis, precursor lesions, and therapy. (J Am Acad Dermatol 2001;45:260-76.)