ABSTRACTA computer-assisted, MRI-based technique of tumor volume determination was used to correlate preoperative hearing levels and long-term postoperative facial function with acoustic neuroma volume. Preoperative hearing was studied in a group of 41 patients subjected to direct tumor volume calculations and in another group of 131 patients in whom volume was extrapolated from the acoustic neuroma volume-diameter relation. Similarly postoperative facial function was correlated with acoustic neuroma volume in another 864 patients in whom long-term follow-up was available. Preoperative hearing levels were found not to be significantly related to tumor volume. However, postoperative facial function was significantly associated with tumor volume and was best predicted as a nonlinear function of diameter. Thus, tumor volume changes are important considerations in the clinical management of acoustic neuromas. Patients should be advised that even small changes in tumor diameter (especially in larger tumors) can result in tumor volume changes that may be associated with significant changes in postoperative facial function.