We evaluated central, temporal, and cortical atrophy by linear measurements on brain computed tomography (CT) in 17 patients with moderate to severe histologically verified Alzheimer disease (AD) compared with findings in 84 nondemented elderly controls. Measurements were adjusted for age and head size. The AD patients had wider third and lateral ventricles as well as larger temporal horns and Sylvian fissures compared with controls. Cortical atrophy tended also to be more pronounced for AD patients relative to controls. Thus measures of central and temporal atrophy clearly distinguished AD patients from normal aged individuals. In AD patients, the width of the third ventricle was significantly correlated with the choline acetyltransferase (ChAT) activity in the post-mortem frontal cortex (r= 0.65,p= 0.005) and in the temporal cortex (r= 0.59,p= 0.006). CT measures did not correlate significantly with neurofibrillary tangle or senile plaque scores. The result suggests that the width of the third ventricle better reflects the degree of cholinergic deficit than severity of histopathological changes, scores of plaques, and tangles in AD.