Publisher Summary This chapter examines the different aspects of HCG positive seminoma. The contrary statements about the prognosis of HCG-positive seminoma lead to severe insecurities about adequate treatment. The course of HCG-negative seminomas from 14 co-operating hospitals was recorded retrospectively to compare them with HCG-positive cases. It was found that 438 patients were included in the study. Fifty of them had elevated HCG values in blood from the testicular vein and 10 had positive immunohistochemistry staining. Three hundred and seventy-eight patients with positive HCG measured in the peripheral blood were compared to 348 patients with normal values. The latter patients were registered from 14 of 96 participating hospitals during the same time period. Elevated HCG in seminoma patients reflects the tumor volume. The number of metastatic patients with a minimum follow-up of 24 months is small and one can state that there is no prognostic difference between HCG-positive and HCG negative seminomas. It is observed that in stage IIB, both groups show poor results following radiotherapy.