We have tested a simple and reliable measure of visuospatial ability in Alzheimer patients--the Clock Drawing Test. To determine the usefulness of this measure, we asked 67 Alzheimer patients and 83 normal controls to draw the face of a clock reading the time of 2:45. Six independent observers blindly evaluated the results with ratings from 10 (best) to 1 (worst). The mean performance score of Alzheimer subjects was 4.9 +/- 2.7 compared to 8.7 +/- 1.1 for normal controls (P less than .001). Inter-rater reliability for the clocks drawn by Alzheimer patients was highly significant (r = 0.86; P less than .001), and there was relatively little overlap between ratings for Alzheimer patients and normal controls. Furthermore, correlations were highly significant (P less than .001) between the mean score of clock drawings and three independent global measures of dementia severity. Although the Clock Drawing Test is certainly not a definitive indicator of Alzheimer's disease, the test is easy to administer and provides a useful measure of dementia severity for both research and office settings where sophisticated neuropsychological testing is not available.