In a series of 177 patients with ruptured supratentorial aneurysms we studied retrospectively the results of early and delayed operation without aggressive removal of subarachnoid blood clots but ventricular and cisternal drainage. The early and delayed groups were comparable demographically and neurologically. The overall results for the early group were a good outcome in 65%, poor outcome in 10% and death in 24%, compared to 53, 20 and 27% respectively in the delayed group. Thus, patients with an early operation and CSF drainage had better results. Permanent ischaemic neurological deficits due to cerebral vasospasm accounted for the poor outcome in 10 and 21% of the patients in the early and delayed groups, respectively and rebleeding accounted for the poor outcome in 5 and 10% in the early and delayed groups respectively. The mean amount of haemoglobin in the cerebrospinal fluid from cisternal drainage was 6.4 g, corresponding to about 40 ml of whole blood, during the 12-day period after SAH. The level was higher in patients with larger subarachnoid clots or with symptomatic vasospasm than in those with smaller clots or without such vasospasm. Early operation combined with ventricular and cisternal drainage is considered to be a useful surgical method for patient with a ruptured aneurysm.