AbstractThe results and complications of neurovascular operations in one surgeon's experience during the era of the operating microscope are reviewed in the framework of the pathophysiology of the illness for which they were performed. Overall mortality rate was 5% and morbidity rate 11% in 405 patients with intracranial aneurysms. Morbidity and mortality varied according to preoperative neurological function, location and size of aneurysm, and number of days from last subarachnoid hemorrhage to surgery. Although a delay in operation improved the operative results, there were significant mortality and morbidity among patients awaiting surgery. There were immediate and delayed ischemic complications. In the former group (7% of cases), the cause was clearly attributable to surgical trauma, such as damage to perforating vessels and major vessel occlusion, which was related to size and location of the aneurysm and unrelated to the patient's neurological function or timing of surgery. Delayed ischcmic complications, minor and reversible in 10% of patients, severe in 5%, were related to preoperative neurological function and timing of surgery. These did not occur in any patients operated on for a mass effect from the aneurysm without a subarachnoid hemorrhage.The overall combined major morbidity and mortality for carotid endarterectomy in 681 patients in whom the microscope was not used was 2%, but varied according to medical, neurological, and angiographically determined risk factors. Patients were seldom operated on for lesions that did not produce at least a 70–80% stenosis unless there was angiographie evidence of severe ulccration. All patients were monitored intraoperatively with cerebral blood flow measurements and a continuous electroencephalogram. Retinal artery pressure measurements were performed pre‐operatively and postoperatively. The relationship of these monitoring techniques to the pathophysiology of ischemic symptomatology is reviewed.Preliminary evaluation of 149 extracranial to intracranial bypass procedures for occlusive disease of the carotid system, and of 22 procedures for occlusive disease in the vertebral‐basilar system indicates a patency rate of 95% and 90%, respectively. The effectiveness of these operations was related to the symptomatology for which they were performed. The overall combined morbidity and mortality was 5%, but varied according to preoperative neurological function.There were 59 operations for cerebral arteriovenous malformations (AVM) (38 parenchymal, 1 death; 21 durai, 1 death). Low morbidity and mortality rates were achieved in parenchymal AVMs by not operating on large lesions or those with a thalamic component and, therefore, these results must be placed in that perspective. This conservative approach was justified by the current lack of information concerning the natural history of this illness. In contrast, virtually all durai AVMs were eventually operated on because of the progressive nature of this acquired illness.