We present a rare case of endometriosis of the cervix. Transvaginal sonography showed a 35-mm cyst in the cervix with diffuse, low-level internal echoes. Transvaginal sonography-guided aspiration with a 17-gauge needle was performed, yielding a very thick chocolate-colored fluid. Cytological examination of the fluid revealed the presence of endometrial cells. Symptoms resolved after aspiration and no recurrence has developed.