We report a case of adult sacrococcygeal teratoma resected by an abdominosacral approach. A cystic mass 13 cm in diameter in the pelvic cavity and left hydronephrosis were detected incidentally by abdominal computed tomographic (CT) scan in a 55-year-old man. The pelvic tumor extending from the presacral area to the coccyx was resected via a combined abdominal and transsacral approach. The resected specimen weighed 700 g and the pathological diagnosis was mature teratoma. While the sacrococcygeal area is the most frequent site of teratoma in infants, it is a rare site in adults. This is to our knowledge, the 30th case report of adult sacrococcygeal teratoma in Japan. At one month after the operation the patient had no bowel dysfunction and no dysbasia, but he had mild bladder dysfunction requiring self-catheterization twice a day at twelve months. The patient had no evidence of disease at twenty months after the operation.