In this study, a statistical evaluation of the hearing improvement, the incidence of postoperative tinnitus and vertigo, and the permanency of the surgically restored hearing of 120 women and 80 men operated on for otosclerosis between 1970 and 1971 was undertaken. The standardized operating procedure in all of these cases involved the use of a Gelfoam and wire prosthesis (Schuknecht 3). All patients underwent normal audiological examinations, including determination of bone and air conduction values. Pure tone thresholds were determined by averaging the values for 500, 1,000, 2,000 and 4,000 Hz. The incidence (10%) of severe sensorineural loss in regard to age, preoperative bone conduction, and oval window pathology was examined. Severe sensorineural losses had occurred immediately postoperatively in 14 of the ears. In the remaining ears, losses were gradual in the course of 15 years. Hearing thresholds in ears not subjected to operation were also determined.