CT and MR appearance of the brain in three children with ornithine transcarbamylase (OTC) deficiency aredescribed. They showed clinical signs of vomiting and convulsion and were diagnosed by measurement of plasmaammonium, amino acids, acid-base balance, and urinary orotic acid levels. CT and MR were performed within onemonth from the onset of the symptom. CT and MRI demonstrated brain swelling with small ventricles and diffuse lowdensity of white matter, which indicates cerebral hypoperfusion secondary to elevated intracranial pressures. Withmore prolonged survival hyperammonemia may cause cerebral atrophy. CT and MR appearance in these cases resembled ahypoxic brain damage and this finding should be included in the differential diagnosis.