A 28-year-old male presented with a small painless lump in his left hemiscrotum. A physical examination revealed a non-tender mass that was palpable on the tail of left epididymis, and the testis and spermatic cord were normal. Ultrasonography showed an isoechoic round shaped tumor, 16 mm in diameter. An exploration of the scrotum was performed, based on a preoperative diagnosis of a left epididymal tumor. The tumor was located below the tail of epididymis, and had a whitish capsule, which looked similar to tunica albuginea testis. A frozen section revealed testicular tissue without any malignant change, and therefore polyorchidism was diagnosed. The accessory testis was resected because there was no connection with the epididymis and vas deferens. Polyorchidism is a rare congenital anomaly with 24 cases reported in the Japanese literature. The indications for the resection of an accessory testis are controversial. Patients with intrascrotal polyorchidism might be recommended to undergo a resection of the accessory testes if there are signs of dysplasia during an intraoperative biopsy. Patients must be followed up with regular clinical and ultrasonic examinations when accessory testes are preserved. However, extrascrotal supernumerary testes should be managed by an orchiectomy because of the increased risk of malignancy.