Testicular tumors and malignant lymphomas are, with increasing incidence, the most frequent malignant diseases in men between the age of 15 and 34. With the introduction of cisplatin-based polychemotherapy, cure rates rose to over 90% in patients with germ cell tumors and were comparably favorable at around 80% in those with malignant lymphomas. In view of these high cure rates, increasing clinical importance is attached to chemotherapyinduced fertility disorders. One problem involved in assessing the influence of chemotherapy on fertility is the fact that the malignant disease itself strongly alters spermatogenesis. This complicates an evaluation of the effect of cytostatic therapy on fertility disorders. There are significant cytostatic- and dose-specific differences. Longterm infertility due to cytostatic therapy may be expected in more than 50% of the patients at a cumulative dose of cisplatin > 0.6 g/m2, cyclophosphamide > 6 g/m2, and procarbazine ≧ 4 g/m2. However, it takes up to 3 years or more for spermatogenesis to recover after the termination of chemotherapy. An individual assessment of the post-therapeutic fertility status is extremely limited, since variance of the pretherapeutic fertility status causes interindividual differences, and the numerical data mentioned above only permit a vague estimation. Before patients undergo cytostatic therapy, cryopreservation of germ cells should thus be suggested or, in some cases, testicular extraction of spermatozoa.