The present study extended previous work on olfactory dysfunction (odor identification deficits) by using the Pocket Smell Test (PST) to discriminate between groups of patients with Alzheimer's disease (AD), vascular dementia (VaD), and major depression (MD). Sixty patients meeting the DSM-IV criteria for either AD, VaD, or MD (20 per group) underwent assessment with the PST, a three-item screening measure of odor identification, and the Mini-Mental State Examination (MMSE). Patients with AD scored significantly lower than patients with either VaD or MD on the PST, even after controlling for MMSE scores. A PST score of > or =1 (i.e., 1 or 0 correct) discriminated between patients with and without AD with a classification accuracy of 95% (sensitivity 100%, specificity 92.5%). Olfactory assessment may be of diagnostic utility in the differential diagnosis of AD versus VaD versus MD in elderly patients.