The principal epidemiologic studies of ionizing radiation and skin cancer have all shown that radiation causes basal cell carcinoma but have not found dose-related excesses of squamous cell carcinoma or malignant melanoma. The Japanese atomic bomb study indicates that doses of radiation under about 1 Gy confer less risk per unit dose than higher doses do. All available studies show that skin cancer risk is greater from radiation exposure at young ages than at older ages. Finding few excess skin cancers among irradiated African-Americans as compared to Caucasians with a comparable dose indicates that skin susceptibility to ultraviolet exposure modifies the excess risk from ionizing radiation. Available evidence indicates that the excess risk of skin cancer lasts for 45 years or more following irradiation. Several studies indicate a risk of nonmelanoma skin cancer (NMSC) following cancer therapy; however, most of the studies reporting on NMSC have not distinguished between patients who received radiotherapy versus chemotherapy. Some, but not all, follow-up studies of cancer patients have reported excesses of malignant melanoma as second malignant neoplasms. It is not clear from the studies how much, if any, of the excess melanoma risk is attributable to radiotherapy. Med. Pediatr. Oncol. 36:549–554, 2001. © 2001 Wiley-Liss, Inc.