With the development of computed cranial tomography (CCT), many physicians have come to rely on this technique as their sole means of excluding a diagnosis of acoustic neurinoma. In our series of 237 patients with acoustic tumors, 29% of tumors were not detected by CCT. New thin-section scanners improve this detection rate. Tumors within the internal auditory canal, however, will not be detected without special techniques. We recommend that contrast studies of the posterior fossa be employed to exclude definitely the diagnosis of acoustic tumor when one is suspected.