More than half of the patients with testicular germ-cell cancer show impaired spermatogenesis before undergoing cytotoxic treatment. The known pre-treatment infertility and the reversibility of the fertility problems observed in some after successful anti-cancer treatment have so far prevented an assessment of the true role of cytotoxic therapy in long-term fertility. The introduction of wait-and-see strategies (surveillance) for testicular cancer patients and recent prospective trials comparing patients with and without cytotoxic treatment have provided the means for estimating the extent to which treatment itself affects long-term fertility. Whether or not spermatogenesis is irreversibly impaired by chemotherapy is determined by the cumulative dose of cisplatin: at doses below 400 mg/m2, long-term effects on sperm production as well as on endocrine function are unlikely to occur. Higher doses should be expected to cause long-term losses of exocrine and endocrine gonadal function. In contrast, for adjuvant retroperitoneal radiotherapy in stage I seminoma patients, no data are available comparing long-term gonadal function with patients on surveillance. However, using modern radiation techniques, radiation doses to the para-aortic field (< 30 Gy) and testis shielding providing testis scatter radiation (< 30 cG), radiation-induced impairment of fertility is very unlikely.