We herein report a case of idiopathic testicular infarction. The patient was a 20-year-old man with the chief complaint of right testicular swelling and pain. Ultrasonography and color Doppler sonography demonstrated a hypoechoic lesion without any blood supply. Torsion of the right spermatic cord was most suspected, but we could not exclude the possibility of testicular cancer judging from the findings obtained by computed tomography and magnetic resonance imaging. Surgical exploration did not reveal any torsion of the spermatic cord. Subsequently, right high orchiectomy was performed because of the risk of a testicular cancer. Histopathological examination revealed a hemorrhage and congestion of the testis and epididymis.