When the clinical diagnosis is in doubt, biopsies obtained from areas suspicious for tumor of the testis can be examined using frozen sections after prior inguinal clamping. The correct tumor diagnosis was established in 81% of cases in the first biopsy, and in 11% in the repeat biopsy, making a total of 93% (n = 70). Frozen section examination is of considerably greater importance within the framework of lymphadenectomy in patients with non-seminomatous testicular tumours. In 1014 of such frozen section examinations, 98.4% of the frozen section findings were correct, 0.3% undecided and 1.3% false. The diagnostic sensitivity was 100%, the diagnostic specifity 98.6%, the technical sensitivity 84%, the technical specifity 99.8%. Lymph node metastases of up to 2 mm are only rarely detected by frozen section; for sizes between 2.1 and 10 mm, they are recognized in 85% of cases. In the setting of lymphadenectomy, the frozen section examination can be employed to monitor the extent of the dissection.