Sunlight, particularly its UVB component, is thought to be the most important environmental factor for oncogenesis of melanoma. Its intensity, at the ground level, is a positive function of altitude and a negative function of latitude. Sun exposure and susceptibility in childhood seem to be major risk factors at least in Anglo-saxon countries. UV radiations are able to act as complete carcinogen. Eumelanin/pheomelanin ratio also appears as an important risk factor. Ionizing radiations, heat and traumas have been seldom related to melanoma carcinogenesis. Several chemicals, among them drugs and toxic drugs, add to the list of possible causative agents. Loss of alleles encoding for suppressor factors, caused by UV radiation, might play a significant role in carcinogenesis. A model is proposed, for "mediterranean" vs "caledonian" melanoma, in which the phenotypic sequence melanocytic nevus----melanoma would exhibit peculiar characteristics.