With increasing numbers of survivors from cancer at a young age, the issue of fertility preservation has assumed greater importance. This review describes normal ovarian and testicular function and summarizes what is known about the effect of chemotherapy and radiotherapy on the gonads and uterus. All young patients with cancer or leukemia should have their fertility prognosis discussed before the initiation of treatment. Sperm and embryo cryopreservation should be considered standard practice and be widely available for those at significant risk of infertility. For prepubertal girls, ovarian tissue cryopreservation should be considered if the risk of premature menopause is high, but for the prepubertal boy there are no established techniques in current practice. © 2011 American Cancer Society