This Ontario province-wide cohort study was conducted to compare the risk of adverse pregnancy outcomes in female childhood cancer survivors who received abdominal-pelvic radiation and/or chemotherapy with alkylating agents with the risk among those who were treated by non-sterilizing alkylating agents with the risk among those who were treated by non-sterilizing surgery only. Females in Ontario, Canada, diagnosed in 1964-1988 before age 20 with a histologically confirmed malignancy and who had survived for at least 5 years, attained age 18, and were alive at the time of study, were identified through the Ontario Cancer Registry. We ascertained pregnancy outcomes by a telephone-administered questionnaire. Treatment data were abstracted from medical records for 830 subjects 18-49 years of age, the analysis comprised 340 survivors who had one or more pregnancies after treatment. There was no evidence of an increased risk of having a spontaneous abortion or an infant with a birth defect. Survivors receiving abdominal-pelvic radiation were more likely to have a low birth weight infant (odds ratio estimate [OR] = 3.64; 95% confidence interval [CI] = 1.33-9.96), a premature low birth weight infant (OR = 3.29; 95% CI = 0.97-11.1), or an infant who died in the perinatal period (OR = 2.41; 95% CI = 0.50-11.5), compared with those receiving surgery. Risks of perinatal death and having a low birth weight infant increased with dose of radiotherapy directed to the abdomen.