The object of the study was to evaluate brain tissue oxygenation (p(ti)O2) for intra-operative monitoring of critical ischemic events during early cerebral aneurysm surgery of the anterior circulation supplementary to somatosensory evoked potentials (SEPs). P(ti)O2 was continuously evaluated during surgery for an intracranial aneurysm in 28 patients. Standard cortical SEP monitoring was simultaneously performed. The two monitoring methods were compared by evaluating their respective responses to intra-operative events (particularly temporary vessel occlusion), clinical and neuroradiological outcome. P(ti)O2 and SEPs were reliably used for monitoring in 16 patients. Seven patients were excluded due to too high or too low p(ti)O2 readings or initial absence of SEPs (six patients). Of 64 intra-operative events 19 events (eight patients) were associated with a significant decrease in p(ti)O2 (below 10 mmHg), 22 events (13 patients) were associated with a significant change in SEP amplitude (< 50% decrease related to baseline). Temporary vessel occlusion (six SEP andp(ti)O2 changes each in eightpatients) and surgical dissection were most likely to be followed by significant changes in a monitoring method. Intra-operative p(ti)O2 was found to be a safe, rapid method for documenting ischemic events. P(ti)O2 was found to supplement SEP monitoring. The use of p(ti)O2 measurement as a routine monitoring method in aneurysm surgery is limited by its focal spatial resolution. Nevertheless, it might be helpful as an adjunct in situations when SEPs are absent at baseline, in aneurysms when parent vessel anatomy is complex or if temporary vessel occlusion is planned.