The incidence and mortality rates of malignant melanoma in Caucasians are increasing rapidly in many countries worldwide. Considerable circumstantial evidence suggests that exposure to solar radiation may play a role in this substantial rise in malignant melanoma. This evidence comes primarily from epidemiologic studies and from the identification of susceptible phenotypes. Despite the increasing data that implicate sunlight as an important factor in the development of certain types of malignant melanomas in humans, the role of solar electromagnetic radiation in the pathogenesis of human malignant melanomas is yet to be determined.