BACKGROUND: Insofar as a majority of children with malignant diseases are cured, the late effects of treatment are of major importance. PROCEDURE: A retrospective study was conducted of gonadal and sexual function of 77 adult male survivors of childhood malignancies treated and cured at a single center from 1970 to 1989 and followed for a median of 13 years. The study included an interview, physical examination, sperm test, and hormonal analyses. RESULTS: One-third of the patients were treated for hematological malignancies, one-third for CNS tumors, and one-third for other malignancies. Eleven patients required androgen substitution after treatment for tumors of the pituitary-hypothalamic region or acute lymphoblastic leukemia including testicular irradiation and/or orchiectomy. In three patients the testicles were removed. The other eight had small testicles, and those providing sperm samples had azoospermia, and sexual function was disturbed in most of them. Most of the remaining 66 patients had small testicles. Normozoospermia was found in 63%, oligozoospermia in 20%, and azoospermia in 17%. Although there was a highly significant correlation between testicular volume and sperm test, 25% of patients with testicles of