A case of mitochondrial encephalomyopathy (MEM) followed-up by MRI for 2 1/2 y is presented. MRI showed gross, diffusely distributed white matter lesions in both hemispheres predominantly in frontal, parietal, temporal and occipital locations a marked ventriculomegaly indicative of cerebral atrophy. Except a slight increase of the cerebral atrophy there were no changes in the follow-up examinations. There are no specific MRI findings in MEM, the diagnosis is established by the synopsis of MRI, laboratory data and muscle biopsy.