The series studied comprises all 851 patients with symptom-producing intracranial saccular aneurysms admitted to the departments of neurosurgery in Denmark in the five-year period of 1970-1974. The series was divided into seven clinical stages according to Hunt's classification. More than half of the patients were grouped in stages IV and V (Hunt grade 2-3). Of the patients, 76% were found primarily suitable for operation. The mortality within the individual stages was to a great extent independent of the time of operation. A total of 94% of the aneurysms were localized within the region of the carotid artery, with a roughly equal distribution among the internal carotid, anterior communicating, and middle cerebral arteries. Multiple aneurysms were found in 19% of the patients subjected to panangiography. There was a distinct correlation between the severity of the spasms and the clinical condition. The course of operation was complicated in 49% of the patients, the complications being equally distributed within the various clinical stages. The mortality for the patients who underwent operation (total 567) was 32%, and 80% of the deaths were due to direct or indirect consequences of aneurysmal bleeding. At the follow-up performed two to seven years after operation, 52% of the survivors were fully capacitated, 20% were partly capacitated, and 28% were incapacitated. Based on a retrospective analysis, we have started a comprehensive prospective study with registration of available parameters in patients with saccular aneurysms admitted to all departments of neurosurgery in Denmark.