The incidence of malignant melanoma has increased markedly in recent years in Norway, and in other countries. Epidemiologic studies show that important risk markers are familial occurrence, skin type, number of regular nevi and presence of dysplastic nevi. The ultraviolet component of sunlight is an important etiologic factor, especially acute intermittent sun-burn experienced during childhood. Some of the melanomas are familial, and genetic markers can perhaps be used in screening. Finally, health education is a very important tool in reducing incidence of melanoma and mortality from this disease. In each single patient, data from cellular and molecular research can assist in making a precise diagnosis and in estimating prognosis.