A 5-month-old male infant was referred to us for evaluation of progressive hypotonia. He had growth retardation, feeding difficulty and general weakness. Brain sonography and computed tomography demonstrated symmetrical lesions in the caudate, lenticular nuclei, thalamus and hypothalamus, suggesting bilateral necrosis. Lactate and pyruvate levels in the blood and cerebral spinal fluid were persistently elevated. A biopsy of the quadriceps muscle showed increased subsarcolemmal mitochondrial enzyme activity on light microscopy. Electron microscopy of the muscle showed deformed and bizarre mitochondria. The patient eventually died at the age of 8 months. Autopsy showed bilateral necrotic foci in the caudate, lenticular nuclei, thalamus, hypothalamus, midbrain, and pons. Histopathologic findings included spongiform degeneration of the affected brain tissue. The characteristic clinical and pathological findings confirmed this case as subacute necrotizing encephalo-myelopathy of Leigh's type. To our knowledge, this is the first autopsy-proven case of Leigh's disease in Taiwan.