The skeletal effects of megavoltage irradiation (60Co) in 25 long term survivors of Wilms' tumor are described. In general, the changes seen with megavoltage irradiation are as frequent but not as severe as those previously reported after orthovoltage irradiation. Vertebral body changes generally occur within 5 years after irradiation. Scoliosis and/or kyphosis do not usually develop until after five years postirradiation. Kyphotic curves tend to progress after the adolescent growth spurt while scoliotic curves do not. Other bony and nonosseous changes are detailed.