OBJECTIVE: Research on the efficacy of antidepressant therapy for depressive symptoms in Alzheimer disease has been hampered by lack of systematic diagnosis, small sample sizes, and short-term follow up. To address these issues, the authors present the design of the Depression in Alzheimer's Disease Study-2 (DIADS-2), a randomized, placebo-controlled multicenter trial to evaluate the efficacy and safety of the selective serotonin reuptake inhibitor sertraline for the treatment of depression in people with Alzheimer disease. METHODS: The authors present and discuss the following important aspects of the design: the inclusion of structured psychosocial therapy for the caregivers of all participants; the measurement not only of patient mood outcomes, but also of global and functional outcomes for patients and mood and burden outcomes for caregivers; the ongoing rating of multiple diagnostic criteria to allow nosologic study of depression in Alzheimer disease; the evaluation of both short-term efficacy and longer-term outcomes; the follow up of all patients regardless of whether they complete study treatment; and the unmasking of treatment assignment at the conclusion of each patient's treatment phase. CONCLUSIONS: The authors believe these design elements are important features to be included in trials of depression and other neuropsychiatric disturbances in Alzheimer disease.