Three patients are reported with a neurological disorder in which hypokinesia and rigidity were the most prominent clinical signs. On CT scan and MRI, two were found to have bilateral lesions in the striatum, mainly in the putamen, and the third had bilateral lesions in the posterior limb of the internal capsule. Laboratory investigations suggested abnormal pyruvate metabolism in all three cases, which was confirmed to skeletal muscle in two cases. In the third the cause was a NADH dehydrogenase defect. The signs and symptoms, the bilateral striatal lesions in two of the patients, and the abnormal pyruvate metabolism justify a classification of mitochondrial encephalomyopathy, resembling Leigh syndrome. This diagnosis must be considered for infants and children presenting with Parkinsonian signs, and mitochondrial energy metabolism should be investigated.