= Abstract =MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) is a rare and currently incompletely defined mitochondrial disease involving mainly muscle and brain. We have recently seen a 17-year-old male patient who, we believe, is the first Korean case. The patient showed the classical picture of MELAS: short stature, generalized limb weakness, lactic acidemia, basal ganglia calcification, migraine-like headache and recurrent strokes with subsequent hemiparesis, hemianopia, and seizures. Electronmicroscopic examination confirmed the diagnosis by demonstrating numerous abnormal muscle mitochondria which contained paracrystalline inclusion bodies. A brief discussion of current status, inherent problems, and possible pathogenic mechanisms of this syndrome will conclude our report.