Hypertension as a risk factor for epilepsy after aneurysmal subarachnoid hemorrhage and surgery. A prospective, consecutive series of 307 patients with aneurysmal subarachnoid hemorrhage ranging from Grades 1 to V according to the classification of Hunt and Hess on admission were evaluated to determine the incidence of epilepsy 1 to 3 years (mean, 1.4 years) after aneurysmal subarachnoid hemorrhage (SAH) and surgery. Sixty-three patients had died and one patient was lost to follow-up. Twenty-nine patients developed epileptic seizures after the SAH and surgery. The mean time from the SAH to epileptic seizure varied from 0 days (day of the SAH) to 2 years (mean, 6.7 months). The seizures were classified as focal in 9 patients (31%) and as generalized in 20 patients (69%). All patients received anticonvulsant medication after more than one seizure. The risk factors for development of posthemorrhagic/postoperative epilepsy were, in order of importance: a history of hypertension; an infarct on late computed tomographic scan; and the duration of coma after the ictus. Of the 85 patients with histories of hypertension, 17 (20.0%) developed epilepsy. Only 12 (5.4%) of the 222 nonhypertensive patients developed epileptic seizures. The difference between the groups was significant (P = 0.0001). Computed tomographic scans were undertaken in 237 patients 1 to 3 years (mean, 1.4 years) after the SAH and surgery. Postoperative epilepsy was significantly associated with infarcts visualized on computed tomographic scan (P = 0.0005). 