We studied the deliveries of female cancer survivors and female siblings in a population-based setting in Finland. Nationwide cancer and birth registries were merged to identify 1,309 first postdiagnosis deliveries of early-onset (diagnosed under age 35) female patients with cancer and 5,916 first deliveries of female siblings occurring in 1987-2006. Multiple logistic regression models were used to estimate risk of preterm (<37 weeks), low birth weight (<2500 g) and small-for-gestational-age deliveries. The risk of preterm delivery among cancer survivors compared with siblings was overall increased [odds ratio (OR) 1.46, 95% confidence interval (CI) 1.14-1.85], the increase in risk being visible in all diagnostic age groups. Risk of low birth weight (LBW) was also significantly increased (OR 1.68; 95% CI 1.29-2.18) but not after adjustment for duration of pregnancy (OR 1.11; 95% CI 0.76-1.64). Neither was the risk of small-for-gestational-age (SGA) increased. The risk of preterm delivery was most pronounced in survivors delivering 10 years or more after diagnosis. Site-specific analyses indicated that survivors of germ cell tumors and central nervous system (CNS) tumors were at increased risk of preterm delivery, although numbers were small. In childhood survivors, kidney tumors formed the main cause of preterm delivery. Pediatric, adolescent and young adult cancer survivors are at risk for preterm delivery. Heightened surveillance is recommended especially for Wilms', germ cell and CNS tumor survivors. Such adverse pregnancy outcomes can occur a decade or more after cancer diagnosis, indicating a continued need for obstetric awareness, surveillance and counseling in former patients with cancer.