Delayed ischaemia due to cerebral 'vasospasm' is a significant cause of morbidity and mortality after aneurysm haemorrhage. In a literature review more than 30 000 cases were found where vasospasm after subarachnoid haemorrhage (SAH) was discussed. The incidence of angiographic vasospasm was 43.3% overall, and 67.3% where angiography was done at a time of maximum expected spasm. Symptomatic vasospasm or delayed ischaemic deficit (DID) occurred in 32.5%. There was no difference in incidence and time course between preoperative and postoperative cases. 30% of those with DID died, and permanent neurological deficits occurred in 34%. A fatal outcome was much more likely in the presence of vasospasm, and a satisfactory outcome one third less likely. Vasospasm is thus the cause of death in about 10%, and of disability in slightly more cases of aneurysmal SAH. The extent of the problem has not changed significantly over three decades.