Eleven of 605 (1.82%) patients evaluated at this Cancer Hospital for testicular germ cell malignancy between 1958 and 1992 had evidence of bilateral testicular malignancy. The age ranged from 28 to 72 years. Five patients had a history of undescended testes and one of them was surgically corrected at age of 11 years. Four of these were synchronous and seven metachronous. Histologically, all four synchronous tumors were pure seminoma. Two of seven metachronous tumor cases had unilateral testicular non-seminoma. The other 5 patients had pure seminoma. The second tumor was diagnosed between 8 months to 150 months after diagnosis of the first one. Three of 7 (42.9%) patients were diagnosed within 5 years. Two patients with synchronous tumors died within 1 year (3 months and 6 months, respectively). Only one patient with metachronous tumors died of the disease. This study indicates that the overall prognosis and outcome depends on the histologic type and stage of the disease and reemphasizes the low but definite risk for development of a second testicular malignancy.