At present, no randomized, controlled trials are available to guide decisions on prophylaxis or treatment of seizures.2,272 A relatively high percentage of aSAH patients (as many as 26%) experience seizure-like episodes,99,272,273 but it remains unclear whether these episodes are verifiably epileptic in origin.99,274 More recent retrospective reviews suggest a lower seizure inci- dence of 6% to 18%,275 278 and 2 of these studies276,278 found that the majority of such patients reported onset of seizure occurring before medical evaluation. Delayed seizures occurred in 3% to 7% of patients.276,278 Retrospective studies have identified several risk factors for the development of early seizures associated with aSAH, including aneurysm in the middle cerebral artery,279 thickness of aSAH clot,276 associated neurological grade,276 and history of hypertension.98 The mode of treatment for patients with ruptured aneu- rysms also appears to influence the subsequent development of seizures. One study of patients treated by endovascular means reported no periprocedural seizures and a delayed seizure rate of 3%.284 Moreover, extended follow-up of patients enrolled in the ISAT demonstrated a significantly lower incidence of seizures in patients treated with endovas- cular coiling.140 The association between seizures and func- tional outcome remains unclear. Some studies have reported no impact on outcome,276,278 whereas others found seizures to be independently associated with worse outcome.275 Two recent large, retrospective, single-institution studies of pa- tients with aSAH found that nonconvulsive status epilepticus is a very strong predictor of a poor outcome.285,286 Although high-quality evidence for routine anticonvulsant use in aSAH is lacking, short-term prophylactic antiepileptic therapy is still commonly used in patients with aSAH,274,276,278 based on the argument that seizures in acutely ill patients with aSAH could lead to additional injury or rebleeding from an unse- cured aneurysm. 