We studied a patient with somatic growth failure with easy fatigability, myopathy with mitochondrial abnormality, increased lactate and pyruvate in blood and CSF, mental retardation, seizure, myoclonus, deafness, cerebellar ataxia, and blindness with macular degeneration and optic atrophy. Pathologic findings included multiple brain infarctions and massive calcification in the basal ganglia. Biochemical studies of isolated mitochondria revealed decreased oxygen consumption in skeletal muscle, diaphragm, and brain, suggesting an abnormality in the respiratory chain.