This study is an investigation of the concordance among different sources of information on ratings of depression in patients with Alzheimer's disease (AD). Informants were 75 outpatients with diagnosed AD (22 with major depressive disorder), their caregivers, and geriatric clinicians. Clinicians rated each patient on the Hamilton Rating Scale for Depression on the basis of (a) the patient's report, (b) the caregiver's report, and (c) the clinician's evaluation. Overall, patients perceived themselves as less depressed than did caregivers or clinicians; for nondepressed patients, caregivers reported patients less depressed than clinicians reported; for depressed patients, no significant differences were obtained between caregiver or clinician. Certain items were more discrepant among informants and significantly differentiated depressed from nondepressed AD patients. Level of patient dementia did not affect ratings. These findings support the need for comprehensive, accurate assessment of depression in AD patients.