Since the introduction of antineoplastic chemotherapy, lasting clinical remissions have been obtained for many patients with acute lymphoblastic leukemia, Hodgkin's disease, gestational trophoblastic tumors, and other malignancies. With this therapeutic success there have been concerns about persistent or delayed toxicities of cancer chemotherapy that may become clinically significant for long-term survivors. Gonadal toxicity and infertility occur in many men, women, and children treated with antineoplastic drugs. In this paper we review the clinical syndromes of chemotherapy-related gonadal toxicity and discuss how particular drug classes, doses, or combinations correlate with the degree of gonadal injury and with the potential for recovery of function. Further, we examine how drug effects on germ cell production and endocrine function vary with the age of the patient at the time of treatment. Finally, we comment on the need for long-term prospective studies of fertility, teratogenesis, and mutagenesis in patients receiving cancer chemotherapy.