Myeloid sarcoma is a neoplasm of immature granulocytes, monocytes, or both involving any extramedullary site. Myeloid sarcoma involving the testis, however, is uncommon and very rarely occurs as an isolated mass. We describe 4 patients with myeloid sarcoma involving the testis, including 2 patients in whom the neoplasm was isolated to the testis (1 unilateral and 1 bilateral). Histologically, 4 neoplasms were poorly differentiated and 1 was blastic. Each neoplasm was shown to be of myeloid lineage, and negative for T- and B-cell specific antigens using immunohistochemical methods. One case was also positive for chloroacetate esterase. In the literature, most cases of myeloid sarcoma involving the testis represent relapse or the initial presentation of acute myeloid leukemia. Including the 2 cases we report here, only 7 cases of myeloid sarcoma isolated to the testis have been reported.