A retrospective multicenter study was conducted, designed to evaluate the efficacy and safety of midazolam for the treatment of status epilepticus. The subjects were 358 inpatients who received intravenous midazolam therapy for status epilepticus. The mean age was 48.6 +/- 46.5 months. The underlying disorder was epilepsy in 195 cases, and acute symptomatic diseases in 163 (encephalitis or encephalopathy in 88 cases). Midazolam was administered as a bolus dose (0.25 +/- 0.21 mg/kg), followed if necessary by continuous infusion (0.26 +/- 0.25 mg/kg/hr). The bolus injection was effective in 162 (56.6%) of the 286 cases. In the end, seizure suppression was obtained in 231 cases (64.5% of the total). The effectiveness of midazolam was lower in patients in whom midazolam was initiated more than 3 hours after seizure onset, and this tendency was particularly marked in the epilepsy group. During the treatment period, 10 patients died, but none of these deaths were associated with midazolam therapy. The incidence and types of adverse events were consistent with previously reported data. The present results indicate that midazolam is highly effective for the management of status epilepticus, if used sufficiently early after seizure onset.