A child was seen because of encephalopathy and metabolic ketoacidosis at 19 months. She was found to have a cobalamin-responsive form of methylmalonic acidemia of the cbl A complementation group. However, after treatment with cyanocobalamin and a protein-restricted diet, with recovery from the encephalopathy, she was found to have a tremor and bilateral dystonic posturing in association with lucencies in the globus pallidi shown by computed tomographic scan.