Individuals suffering from depression seek help as frequently in the primary care setting as in psychiatric facilities. As primary care physicians increasingly provide such treatments, they will need to assess a patient's clinical status before, during, and after treatment. The authors evaluated the concordance and factor structures of 2 widely used depression inventories, the Beck Depression Inventory and the Hamilton Rating Scale for Depression, in a sample of primary care patients participating in a randomized, control trial of treatments for major depression. The 2 scales were significantly correlated and assessed similar rates of improvement at multiple assessment points. Factor analyses indicated that despite their equivalent assessment of severity of depression, the 2 instruments emphasize different dimensions of depression. Major depression is a common illness among medical outpatients. Studies using structured psychiatric interviews have shown that between 5% and 10% of such individuals suffer from major depression at any given time (Katon & Schulberg, 1992) and that the functional impairment incurred from this disorder is greater than that incurred with many chronic physical illnesses (Wells et al., 1989). Furthermore, this psychiatric disorder is associated with excessive use of health care services (Regier et al., 1988). Given that depressed persons seek help as frequently in the primary care setting as in psychiatric facilities (Regier et al., 1993), clinical guidelines have been developed by the Agency for Health Care Policy and Research (AHCPR) of the U.S. Public Health Service to assist primary care physicians in the diagnosis and treatment of mood disorders (AHCPR, 1993). As internists and family practitioners strive to improve their assessment procedures and to objectively measure the severity of a patient's affective distress before, during, and after treatment, what psychometrically acceptable instruments are available for these tasks? Among the best validated are the clinicianadministered Hamilton Rating Scale for Depression (HRSD; Hamilton, 1960, 1967) and the self-report Beck Depression Inventory (BDI; Beck, 1978; Beck etal., 1961). The HRSD items largely measure somatic and neurovegetative aspects of depression, whereas the BDI items focus more on the disorder's cognitive and affective dimensions. Numerous reports describe the application of these instruments in studies of psychiatric patients and their psychometric