Mitochondrial encephalomyopathy, lactacidosis and stroke-like episode (MELAS) syndrome is a phenotypically and genetically heterogeneous mitochondrial disorder with a clinical onset between the first and third decade. The clinical hallmark is the stroke-like-episode, which mimicks ischemic stroke but is usually transient and non-disabling in nature. The morphological equivalent on MRI is a T2-hyperintensity, predominantly over the temporo-parieto-occipital region, not confined to a vascular territory, which is also hyperintense on diffusion weighted imaging and on apparent diffusion coefficient sequences (vasogenic edema, stroke-like lesion). Additional features include seizures, cognitive decline, psychosis, lactic acidosis, migraine, visual impairment, hearing loss, short stature, diabetes, or myopathy. Muscle biopsy typically shows ragged-red fibers, COX-negative fibers, SDH hyperreactivity, and abnormally shaped mitochondria with paracristalline inclusions. The diagnosis is confirmed by demonstration of a biochemical respiratory chain defect or one of the disease-causing mutations, of which 80 % affect the mitochondrial tRNALeu gene.