A 17-year-old Quarterhorse stallion with left-sided cryptorchidism presented for colic. On ultrasound exam a 16x13cm mass was visualized in the caudal abdomen. At surgery, the mass was seen to be attached via a spermatic cord with a torsion of at least 360 degrees. The mass was removed and on histopathology it was found to be a testicular seminoma without evidence of metastasis. Severe hemorrhage and edema was also seen histologically in the testis and the spermatic cord, consistent with the gross appearance and presumably a result of the spermatic cord torsion. Testicular torsion has been reported in man, pig, dog and stallion. Although usually associated with intra-abdominal testes several cases of scrotal testicular torsion have been reported in man and stallion. Testicular neoplasia is rare in the horse and usually benign. Seminoma is the most common neoplasia of the stallion testis.