The radiological appearance of the internal acoustic meatus, obtained by tomography of the temporal bone, is presented for 115 patients with normal inner-ear function. These patients served as normal controls, and their tomograms are compared with those obtained in 48 patients who were initially suspected of having acoustic neuromas but in whom Pantopaque cisternography was negative. These are also compared with the findings obtained in 59 patients with surgically-verified acoustic neuromas. In normal persons the size of the vertical diameter of the meatus on the two sides, as measured by tomography, differed in only a few cases by more than 1 mm. The results obtained in patients who were suspected of having a neuroma, but in whom Pantopaque cisternography had excluded such a diagnosis, coincided completely with the results found in the normal group, and a difference of more than 1 mm. between the right and left sides is therefore indicative of a pathological process in the internal and acoustic meatus. A normal meatus does not exclude the presence of a tumour, since 10 per cent of patients with neuromas have identical meatus. No evidence of radiological destruction was found, either in the normal material or in the group of patients suspected of having a neuroma. Destruction of the bone surrounding the meatus must therefore be regarded as highly suggestive of the presence of a tumour, but lack of destruction does not exclude a tumor. Tomography of the temporal bone should be applied routinely in the search for acoustic neuromas, in patients with unilateral acoustic or vestibular complaints. The evaluation of the tomograms, however, should be performed by a few, specially interested radiologists.