Postoperative venous infarction following aneurysm surgery was studied in 48 patients with anterior communicating artery aneurysms operated on through the interhemispheric approach at the acute stage of subarachnoid hemorrhage (SAH). Of 23 patients whose bridging veins were sacrificed during surgery, 11 (47.8%) showed venous infarction in the frontal lobes. In contrast, only one (5.9%) of 17 patients whose bridging veins were preserved developed cerebral edema. None of eight patients who were operated on after Day 11 (the day of SAH was defined as Day 0) showed this complication, although bridging veins were sacrificed in six of them. Venous infarction following acute aneurysm surgery tended to occur more frequently in patients of higher SAH grade and/or more advanced age, but these correlations were not significant. However, the correlation between the sacrifice of veins and venous infarction was significant (p less than 0.025). Because this potential complication may compromise the benefit of acute aneurysm surgery and cause damage, it is important to preserve the venous system and in some instances to select another surgical approach based on the pattern of venous drainage in the frontal lobe.