This article focuses on diagnostic and nosologic challenges intrinsic to geriatric depression, including characteristics interfering with symptom and syndrome ascertainment, the impact of medical and cognitive disorders, the usefulness of screening instruments, and barriers imposed by treatment settings. The article also identifies gaps in existing knowledge and outlines a research agenda. Nosologic characterization of depressives syndromes contributed by specific medical disorders may lead to effective strategies for prevention and treatment of depression. Studies need to examine whether treatment of depression can improve the outcome of medical illnesses requiring active patient involvement in treatment. Considering disability a distinct aspect of health status may add an important dimension to the assessment of depression and result in complementary interventions aimed at depression and disability concurrently. The provisional criteria for depression of Alzheimer's disease, if validated, may facilitate treatment research. Studies need to characterize cognitive dysfunctions associated with later development of dementia or poor treatment response in patients with depression. Care managers working together with primary care physicians can improve the recognition and treatment of depressed elderly patients by obtaining the training in using validated instruments and treatment algorithms.