The observations of Skakkebaek and the evolution of the concept of intratubular germ cell neoplasia (or testicular intraepithelial neoplasia (TIN)) indicate that most, but not all, germ cell tumors of the testis evolve from a common neoplastic precursor lesion: intratubular germ cell neoplasia, unclassified type (IGCNU). It is defined as the presence of malignant germ cells within the seminiferous tubules. At 5 years about 50% of patients with a testicular biopsy positive for IGCNU have developed invasive germ cell tumors, and only a small fraction remain free of invasive tumors by 7 years. Orchiectomy is the treatment of choice in patients with unilateral IGCNU, and low-dose radiation is efficacious in patients with bilateral IGCNU (although sterility is certain). So far, there is only one published report of occurrence of two cases of germ cell cancer despite previous local radiotherapy to the testis. A recent study demonstrated an estimated risk of recurrent IGCNU following chemotherapy of 21% and 42% at 5 and 10 years, respectively.