Monitoring of cardiovascular, respiratory, and evoked potential parameters has been advocated during posterior fossa surgery to detect brainstem ischemia that may result from surgical manipulations. We report here our retrospective and smaller prospective experience of spontaneous ventilation as a monitor in patients undergoing vascular surgical procedures in the posterior fossa. Forty patients' charts were reviewed retrospectively, and 10 patients were studied prospectively. Respiratory changes in the retrospectively studied group occurred in 9 patients. Four patients developed apnea during temporary occlusion of the vertebral artery. These respiratory changes were associated with simultaneous cardiovascular changes in only 2 patients, and of the 13 patients monitored with evoked potentials, only 2 had simultaneous evoked potential changes. In the prospectively studied group, respiratory changes occurred in 4 patients. Three patients (2 with apnea during temporary occlusion) had a simultaneous change in evoked potentials but no cardiovascular changes. One patient had a change in all three parameters. Allowing our patients to breathe spontaneously provided an early and rapid indication of brainstem ischemia, especially during the temporary occlusion of the vertebral basilar artery system.