Status epilepticus (SE), both convulsive and nonconvulsive, can arise from diverse etiologies in either a normal brain or a previously epileptic brain. SE has a distinct natural history and unattended can lead to profound, life-threatening, systemic metabolic and physiologic disturbances. These factors may account for the poor prognosis associated with this disorder. However, there is mounting experimental evidence that SE itself, independent of metabolic and physiologic disturbances, leads to lasting brain dysfunction.