Few outcome data are available about convulsive status epilepticus managed in the intensive care unit. We studied 90-day functional outcomes and their determinants in patients with convulsive status epilepticus. Two hundred forty-eight convulsive status epilepticus patients admitted to 18 intensive care units in 2005-2007 were included in a prospective observational cohort study. The main outcome measure was a Glasgow Outcome Scale score of 5 (good recovery) on day 90. Convulsive status epilepticus occurred out of hospital in 177 (67%) patients, and all but 15 patients were still seizing at medical team arrival. The median time from convulsive status epilepticus onset to anticonvulsant drug initiation was 40 mins (interquartile range, 5-80). Total seizure duration was 85 mins (interquartile range, 46.5-180). Convulsive status epilepticus was refractory in 49 (20%) patients. The most common causes of convulsive status epilepticus were anticonvulsive agent withdrawal (36.4%) in patients with previous epilepsy and stroke (27.7%) in inaugural convulsive status epilepticus. Mechanical ventilation was needed in 210 (85%) patients. On day 90, 42 (18.8%) patients were dead, 87 (38.8%) had marked functional impairments (Glasgow Outcome Scale score, 2-4), and 95 (42.4%) had a good recovery (Glasgow Outcome Scale score, 5). Factors showing independent positive associations with poor outcome (Glasgow Outcome Scale score, <5) were older age (odds ratio, 1.04/year; 95% confidence interval, 1.02-1.05; p=.0005), cerebral insult (odds ratio, 2.70; 95% confidence interval, 1.37-5.26; p=.007), longer seizure duration (odds ratio, 1.72/120 min; 95% confidence interval, 1.05-2.86; p=.03), on-scene focal neurologic signs (odds ratio, 2.08; 95% confidence interval, 1.03-4.16; p=.04), and refractory convulsive status epilepticus (odds ratio, 2.70; 95% confidence interval, 1.02-7.14; p=.045). Ninety days after intensive care unit admission for convulsive status epilepticus, half the survivors had severe functional impairments. Longer seizure duration, cerebral insult, and refractory convulsive status epilepticus were strongly associated with poor outcomes, suggesting a role for early neuroprotective strategies.