Sacrococcygeal teratoma is the most common solid tumor to occur in neonates, in whom it mostly takes the form of an obvious exophytic mass. They are, however, rarely found in adults. We report the CT and histopathologic findings of an adult cystic teratoma arising from the lower sacrococcygeal region that was discovered incidentally. Unenhanced CT scans showed an oval-shaped, cystic lesion with hyperattenuating content and no contrast enhancement. After surgery, the gross specimen was seen to be a cystic lesion filled with mucin. Microscopy revealed three germ cell layers in the cystic wall and the lesion was confirmed as cystic teratoma.