O n presentation at a neurosurgical-neurovascular center, patients suffering from aneurysmal subarachnoid hemorrhage (SAH) may exhibit a reduced level of consciousness due to initial bleeding, rebleeding, hydrocephalus, sedation, or seizure 1,9,15,20,22 as well as other conditions. Subarachnoid hemorrhage causes seizures in up to 26% of patients, which occur most commonly within the first 24 hours. 3,9,20,23 Most seizures occur before hospital presentation. 20 The severity of SAH, as graded on scales like the World Federation of Neurosurgical Societies (WFNS) scale, as well as intracerebral hemorrhage (ICH), localization of the aneurysm, and the amount of subarachnoid blood are important risk factors for the development of early seizures. obJect After subarachnoid hemorrhage (SAH), seizure occurs in up to 26% of patients. The impact of seizure on outcome has been studied, yet its impact on grading is unknown. The authors evaluated the impact of early-onset seizures (EOS) on grading of spontaneous SAH and on outcome. methods This retrospective analysis included consecutive patients with SAH who were treated at the NeuroCenter, Inselspital, University Hospital Bern, Switzerland, between January 2005 and December 2010. Demographic data, clinical data, and reports of EOS were recorded. The EOS were defined as seizures occurring within 24 hours after ictus. Patients were graded according to the World Federation of Neurosurgical Societies (WFNS) scale pre- and postresuscitation and dichotomized into good (WFNS I-III) and poor (WFNS IV-V) grades. Outcome was assessed at 6 months by using the modified Rankin Scale (mRS); an mRS score of 0-3 was considered a good outcome and an mRS score of 4-6 was considered a poor outcome. results Forty-one of 425 patients with SAH had EOS. Twenty-seven of those 41 patients (65.9%) had a poor WFNS grade. Twenty-eight (68.3%) achieved a good outcome, 11 (26.8%) had a poor outcome, and 2 (4.9%) were lost to followup. Early-onset seizures were proven in 9 of 16 electroencephalograms. The EOS were associated with poor WFNS grade (OR 2.81, 97.5% CI 1.14-7.46; p = 0.03) and good outcome (OR 4.01, 97.5% CI 1.63-10.53; p = 0.03). Increasing age, hydrocephalus, intracerebral hemorrhage, and intraventricular hemorrhage were associated with poor WFNS grade, whereas only age, intracerebral hemorrhage (p < 0.001), and poor WFNS grade (p < 0.001) were associated with poor outcome. coNclusioNs Patients with EOS were classified significantly more often in a poor grade initially, but then they significantly more often achieved a good outcome. The authors conclude that EOS can negatively influence grading. This might influence decision making for the care of patients with SAH, so grading of patients with EOS should be interpreted with caution.