Abstract Purpose: We used data from the first large-scale overwhelmingly population-based study (a) to quantify the risk of adverse pregnancy outcomes in survivors of childhood cancer in relation to cancer type and treatment and (b) to assess live birth rates relative to the general population. Methods: A questionnaire, including questions inquiring about pregnancy outcomes, was completed by 10,483 survivors. A total of 7,300 pregnancies were reported. Odds ratios (OR) for live birth, miscarriage, termination, stillbirth, premature birth, and low birth weight were calculated for different types of childhood cancer and by whether initial treatment involved chemotherapy and abdominal or brain irradiation. For females, the observed number of live births was compared with that expected based on the general population of England and Wales. Results: Female survivors exposed to abdominal irradiation had a significantly increased OR of delivering preterm [OR, 3.2; 95% confidence interval (95% CI), 2.1-4.7] and producing offspring with a low birth weight (OR, 1.9; 95% CI, 1.1-3.2). An increased OR of miscarriage was also associated with abdominal radiotherapy (OR, 1.4; 95% CI, 1.0-1.9). The number of live births observed from all female survivors was two thirds of that expected (O/E, 0.64; 95% CI, 0.62-0.66) and lowest among survivors treated with brain (O/E, 0.52; 95% CI, 0.48-0.56) and abdominal radiotherapy (O/E, 0.55; 95% CI, 0.50-0.61). Conclusion: Female survivors of childhood cancer treated with abdominal radiotherapy are at 3-fold increased risk of delivering preterm, 2-fold increased risk of low birth weight, and a small increased risk of miscarriage. Overall, female survivors produce considerably fewer offspring than expected, particularly those treated with abdominal or brain radiotherapy. (Cancer Epidemiol Biomarkers Prev 2009;18(8):2239–47)