A 17-year-old man visited our hospital with the chief complaint of painless swelling of the left scrotal content. An elastic hard mass was palpable at the upper pole of the left testis. Left radical orchiectomy was performed. The tumor originated from the epididymis and did not involve the testis or the spermatic cord. Histologically, the tumor was diagnosed as a malignant lymphoma (non-Hodgkin's lymphoma, diffuse mixed cell type, B-cell type). No abnormalities were found in other organs. After establishment of the diagnosis of primary epididymal malignant lymphoma, 3 courses of chemotherapy (adriamycin, vincristine, cyclophosphamide, prednisolone) were performed. No evidence of recurrence or metastasis was found 26 months after surgery.