Three neuroradiologists perceptually evaluated CT of 24 patients with Alzheimer type dementia and 22 normal control subjects and made a dichotomous judgment for each case (i.e., normal control or Alzheimer type dementia). The mean percentage of patients correctly classified was 83.3%. The neuroradiologists also completed perceptual ratings on each scan. Thirteen regions were rated for atrophy on a scale of 0-4. Discriminant function analyses of several sets of perceptual atrophy ratings (optimized on an exploratory set and evaluated on a test set) showed that the perceptual ratings of temporal lobe regions produced an average accuracy of 88.57%. In contrast, only 74.26% of the cases were correctly classified when the discriminant functions were based on perceptual ratings of midventricular and supraventricular areas. Linear measures of atrophy correctly classified only 65.20% of the subjects. The results suggest that atrophy ratings of brain regions that show the characteristic macroscopic neuropathological changes of Alzheimer disease may be used by neuroradiologists to reach more accurate diagnostic decisions.