Leukoses and tumours of the central nervous system (CNS) are the leading malignant neoplasms encountered in the childhood. The combined treatment of these diseases including radiotherapy and polychemotherapy may have negative consequences for the functioning of the male reproductive system. The objective of the present study was to estimate the influence of therapy of acute lymphoblastic leukemia (ALL) and malignant tumours of the posterior cranial fossa (PCF) in the childhood on the endocrine and reproductive systems of the adult men. The study included 17 male patients who had undergone the treatment of PCF neoplasms and 6 men after therapy of ALL. The most widespread disorders in the patients of the former group were the small testicle size and the low inhibin B level. The combined treatment of PCF tumours produced a more pronounced adverse gonadotropic effect than ALL therapy.