Study design Patients with primary BCC and CMM and age-, sex-, and residencematched controls participated in the 2 case-control studies. The subjects were 145 BCC cases and 174 BCC controls, and 168 CMM cases and 176 CMM controls. People younger than 18 years or older than 75 years were excluded. The study was approved by the local Ethics Committee and was performed over the period December 1995 to May 1996. The subjects gave informed consent before participation. All subjects were invited to participate by the same standard letter giving brief information about the study. Subjects were interviewed according to a standardized and pre-tested questionnaire by one of two trained interviewers. Eye colour, hair colour and skin type were assessed and the subjects were interviewed on the use of arti¢ cial tanning devices or sunbathing in the nude which might have raised the buttock pigmentation above the constitutive level. Finally buttock skin pigmentation was measured objectively by a skin re£ ectance apparatus. All interviews and physical examinations were performed at the National University Hospital, Copenhagen, Denmark.