This chapter discusses the impaired fertility in both males and females and adverse pregnancy outcomes following successful treatment of cancer in childhood. The ovaries may be damaged following total body, abdominal or pelvic irradiation and the extent of the damage is related to the radiation dose, fractionation schedule and age at time of treatment. Gonadotrophin deficiency following high-dose cranial irradiation will be manifest as delayed puberty or absent menses, and can be treated by hormone replacement therapy. The uterus is at significant risk of damage following abdominal, pelvic or total body irradiation, in a dose- and age-dependent manner. Within the paediatric and adolescent age group, testicular damage occurs with direct irradiation of the testis. Semen cryopreservation is an established and successful technique for the adult male but is more challenging to carry out in children and teenagers. Following cryopreservation, stored spermatozoa may be used for in vitro fertilisation (IVF).