The evidence for and against a causative association between solar UV radiation and cutaneous malignant melanoma in Caucasians is reviewed. Epidemiological evidence (including descriptive studies of latitude of residence, time and age trends, body site distributions, social class, occupation trends, and case-control studies) and animal experimental data are discussed. On present evidence, solar UV radiation is likely the most important factor in the etiology of cutaneous malignant melanoma in Caucasians, and the effects of UV radiation differ for the various subtypes of melanoma. The needs for further research are also discussed.