To investigate the association between withdrawal from antiepileptic drugs (AEDs) and status epilepticus (SE), we evaluated AED levels at the time of, and prior to, an episode of SE in 65 patients with epilepsy. At least one AED was therapeutic in 65% of patients at the time of SE, and all prescribed AEDs were therapeutic in 48%. Ten patients had subtherapeutic AED levels before, and at the time of, SE. Sixteen patients with previously therapeutic levels (25%) had one or more subtherapeutic AED level at the time of SE. Many of the patients had other acute or remote factors that could be associated with SE, and 46 had had previous episodes of SE. Low AED levels or withdrawal can explain only some cases of SE. Citing AED irregularity as the major cause of SE in patients with epilepsy oversimplifies a complex, poorly understood situation.