We encountered an 11-year-old girl with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) who developed occipital lobe epilepsy at the age of 7 years and 4 months. Thereafter she had repeated status epilepticus associated with stroke-like episodes. Status epilepticus consisted of repetitive complex partial seizures with or without secondarily generalized tonic clonic seizures. The seizures did not respond to conventional anticonvulsive drugs, including diazepam, midazolam, phenytoin, lidocaine, chloral hydrate, and thiamylal sodium, and lasted for several hours (mean 9.5 hours). At the age of 11 years, intravenous infusion of L-arginine (0.5 g/kg body weight) was first given five hours after the onset of status epilepticus. The seizures and electroencephalographic abnormalities improved dramatically. After the introduction of L-arginine, in addition to shortened duration of status epilepticus (mean 3 hours), clinical recovery from the status epilepticus was prompt, and the average hospitalization periods could be shortened. There were no obvious adverse effects, including vomiting, hypotension, and urticaria. Our experience suggests that early intravenous administration of L-arginine may be useful in the treatment of status epilepticus associated with stroke-like episode in patients with MELAS.