The principal factors in the incidence of melanoma are racial susceptibility, skin pigmentation and latitude of domicile. Celts, Norwegians and Swedes all have higher incidences of melanoma than people of similar skin colour living in the same latitude. Skin pigment protects but the pigmented races have higher incidences of melanoma in the less pigmented regions such as the sole of the foot and the various squamous mucosae. There is a direct relationship with latitude of residence and its duration, melanoma incidence being higher with proximity to the equator. Apart from these racial and environmental factors, there seem also to be endogenous factors responsible for familial melanoma and for the development of melanoma in young persons. Multiplicity of primary growths is a feature in familial cases.