The clinicopathologic findings in 37 cases of malignant lymphoma with primary clinical manifestation in the testis were analyzed. Of these cases 34 were classified as histiocytic lymphoma and 3 as lymphocytic lymphoma. Patients usually presented with a painless small testicular mass of short duration. The peak incidence occurred in the fifth through eighth decades. Metachronous testicular involvement was noted in 35 per cent of the cases and simultaneous bilateral involvement in 3 per cent. In 25 per cent of the cases the first manifestation of lymphoma after orchiectomy was in the opposite testis. Regional and distant nodes were equally common sites of lymphoma after orchiectomy. The long-term survival of a few patients after orchiectomy may suggest that some malignant lymphomas are truly primary in the testis. However, the short interval free of disease and the rapid death of most patients imply that most testicular lymphomas are a manifestation of multicentric origin of systemic malignant lymphoma. The over-all 2 and 5-year survival rates were 30 and 20 per cent, respectively. Prospective studies are needed to define the optimal modality of treatment.