The Alzheimer Disease Assessment Scale (ADAS) was administered to 61 patients with dementia of the Alzheimer type (DAT) and 52 elderly controls. The DAT group was subdivided into different severity levels of dementia based on scores from the Mini-Mental State Exam: very mild (greater than or equal to 24), mild (20 to 23), moderate (10 to 19), and severe (0 to 9). The mean scores on the ADAS Cognitive subscale for the four levels of dementia (very mild = 23.1 +/- 7.7, mild = 22.9 +/- 8.9, moderate = 38.6 +/- 9.8, severe = 54.8 +/- 7.6) were statistically different from one another (p less than 0.0001, except very mild vs. mild) and were significantly worse than the scores of the elderly control group (5.5 +/- 2.7, p less than 0.0001, ANOVA). Furthermore, the ADAS Cognitive subscale was highly effective in discriminating individual Alzheimer patients from elderly controls. The ADAS Cognitive score correctly classified 100% of the very mild group, 91% of the entire mild group, and 100% of the moderate and severe groups when a cutoff score of 2 SDs above the control group mean was used. Age and education had only minimal effects on the ADAS Cognitive score. The ADAS is a valuable screening test that only takes 30 min to administer and has utility in both early detection and staging of DAT.