A 55-year-old woman was admitted to our hospital with abrupt onset of chorea-ballism in the right arm and both legs. She had thirst before admission. The blood glucose level was 976 mg/dl, the serum osmolality was 335 mOsm/l, and there was slight ketonuria on admission. Even after normalization of the blood glucose level choreiform movement of the right arm and leg continued. Brain CT showed bilateral and symmetrical high density of the putamen on admission, which diminished at 32 days leaving an area of low density. This suggested that the high density was not calcification. There was no mass affect. Symmetrical high intensity of the bilateral putamen on MR T1-weighted images which was slight on admission increased in intensity after 2 months, but disappeared 4 months after the onset in association with the disappearance of choreiform movement. The abnormality in the putamen was considered to be the cause of her involuntary movements. In nonketotic hyperglycemia, high intensity basal ganglia lesions on T1-weighted MR images have previously not been reported. High intensity in the putamen on T1-weighted MR images in the present case might represent multiple petechial hemorrhages which occurred in association with metabolic disorders including nonketotic hyperglycemia.