All interviews were conducted in person by a trained physician (A.C.G.) during 1980 and 1981. Basic demographic information and phenotypic factors were collected using a standard questionnaire. Phenotypic factors included hair color at 21 years of age (light or medium blond, light or medium brown, red, auburn, dark brown, or black), eye color (brown, blue, gray, hazel, green, or other), skin color on the left forearm (very pale, pale, fair, medium, olive, dark olive, or dark), propensity to freckle after sun exposure, depth of tan after repeated sun exposure (none, light, medium, or dark), propensity to sunburn when exposed for 1 hour in strong sun for the first time in summer (painful burn and peel, burn first and then tan, or tan without burning), and number of nevi on the left forearm (0, 1-4, 5-10, or >10). Numbers of sunburns throughout life and at different anatomical locations were obtained by asking participants to recall all episodes of severe sunburn accompanied with pain lasting more than 48 hours, with or without blisters. We also collected detailed data on all outdoor occupations practiced for more than 6 months and all recreations ever pursued regularly after 10 years of age. Total hours of sun exposure were estimated by summing reported lifetime occupational and recreational sun hours. On interview completion, a clinical examination of the face and arms was performed, and skin, hair, and eye color were graded against standard color charts. Numbers of nevi on the left forearm and solar lentigines (brown to black-brown macular lesions with well-defined if irregular edges and normal skin surface creases) on the backs of the hands (0, 1-4, 5-10, or >10) were assessed, as well as the presence of skin cancers and solar keratoses on the left forearm and face.