This report describes a patient with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes who exhibited a segmental vascular narrowing in the crural segment of the right posterior cerebral artery by magnetic imaging angiography in the acute phase of the first stroke-like episode. The vascular stenosis almost improved on the subsequent neuroimaging study. This result suggested that major cerebral arteries might be occasionally involved in a stroke-like episode in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes).