Although cognitive impairment is commonly included in the clinical manifestation of PSP, the precise nature of these deficits, as well as their anatomical substrates are not clarified. Our, preliminary study and those of others using 99mTc HMPAO brain SPECT or PET showed the derangement of cortical metabolism or blood flow predominantly in frontal area despite the lack of cortical histopathology. To assess the severity and the specific pattern of cognitive impairment in progressive supranuclear palsy(PSP) and its correlation with the regional cerebral perfusion, a neuropsychological battery encompassing measures of intelligence, language functioning, verbal/visual memory, attention, psychomotor speed and dexterity, visuospatial construction, mental flexibility, and concept formation and reasoning ability was administered to patients with PSP and age/sex matched controls. Patients with PSP had significantly diminished K-WAIS IQ scores when compared with control subjects, although the patients still had "average level' IQ scores. And the patients were particularly impaired when a task required executive and attentional procedures such as abstract concept formation, reasoning, and conceptual shifting. In addition, the severity of frontal lobe dysfunction was well correlated with the regional perfusion index of superior frontal cortex. These results suggest the frontal lobe dysfunction may be the relatively specific aspect of cognitive impairment in PSP and well correlates with the regional cerebral perfusion pattern of PSP.