Outcome of pregnancy was reported by 99 patients who were cured of childhood Wilms' tumor at seven pediatric cancer centers during 1931 to 1979. These patients carried or sired 191 singleton pregnancies of at least 20 weeks in duration. Among the 114 pregnancies in women who had received abdominal radiotherapy for Wilms' tumor, an adverse outcome occurred in 34 (30%). There were 17 perinatal deaths (five in premature low-birth-weight infants) and 17 other low-birth-weight infants. Compared with white women in the United States, the irradiated women had an increased perinatal mortality rate (relative risk, 7.9) and an excess of low-birth-weight infants (relative risk, 4.0). In contrast, an adverse outcome was found in two (3%) of the 77 pregnancies in nonirradiated female patients with Wilms' tumor and wives of male patients. The high risk of adverse pregnancy outcome should be considered in the counseling and prenatal care of women who have received abdominal radiotherapy for Wilms' tumor.