Cancer survivors may fear infertility, obstetric problems, and genetic alterations in their offspring. After linkage of three registries the probability of post-treatment parenthood and the risk of obstetric and perinatal problems were estimated in cancer survivors compared to individuals without a cancer diagnosis. A total of 1531 of 13,817 patients had 2307 children after one parent's cancer diagnosis: 972 males had 1479 children and 559 females had 828. A total of 1217 patients (784 males and 433 females) became parents > or =9 months after the diagnosis (1899 births: 1221 to male cancer patients and 678 to female patients). The post-diagnosis parenthood probability was 8% at 5 years, and 14% at 10 years without further increase. Female cancer survivors gave birth to post-diagnosis infants with on average 130 grams lower birth weight and 6 days shorter gestations compared with infants in the non-cancer population. Infants fathered by male cancer survivors did not differ from control infants with respect to birth weight or gestational age. There was no increase in the prevalence of major congenital malformations in the offspring of cancer survivors as compared with the offspring of the non-cancer population. Multiple births and deliveries by cesarean sections were increased. Parenthood after cancer is possible in a significant number of patients, more so for males than females. The risk of major congenital malformations was not increased relative to the non-cancer population, nor was perinatal mortality increased. However, female cancer survivors delivered more preterm births and low-birth-weight infants than what was found in the non-cancer population.