This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables. In our series we have 54 cases of acoustic neuroma proven at surgery and 15 cases with a preoperative diagnosis of acoustic neuroma that revealed no tumor on exploration. It should be pointed out that an exposure of the internal auditory canal was indicated because of imbalance per se whether or not a tumor was present, with the exception of two cases. In two cases there was no vertigo or unsteadiness, so that these patients benefited only in the reassurance in knowing that no tumor was present. The remaining nontumor cases benefited from the relief of imbalance brought about by sectioning the vestibular nerves. Since the onset of the use of iophendylate (Pantopaque) in studying the posterior fossa, there has only been one negative exploration of the internal auditory canal. Furthermore, these studies have failed to reveal only one 6 mm acoustic neuroma. In the meantime, the surgical treatment of