Recent technological advances have led to increased interest in intraoperative evoked potential monitoring. Although theoretically valuable, its precise role remains to be defined, and useful criteria for predicting neurological deficit are not well established. The authors used brain-stem auditory evoked potential (BAEP) monitoring during 21 posterior fossa microvascular decompression procedures to assess the value of this technique in predicting postoperative deficit. The surgeon was notified only if there was complete disappearance of wave V. Although no patients had postoperative deafness, BAEP latencies changed significantly in all cases. In four patients, wave V totally disappeared during cerebellar retraction. The BAEP appears to be a very sensitive monitor of auditory function, such that "false positive" results will be frequent if latency criteria alone are used to trigger alterations in surgical technique.