To evaluate the usefulness of case-finding instruments for identifying patients with major depression in primary care settings. A MEDLINE search of the English-language medical literature; bibliographies of selected papers; and experts. Studies that were done in primary care settings with unselected patients and that compared case-finding instruments with accepted diagnostic criterion standards for major depression were selected. 9 case-finding instruments were assessed in 18 studies. More than 15,000 patients received screening with a case-finding instrument; approximately 5300 of these received criterion standard assessment. Case-finding instruments ranged in length from 2 to 28 questions. Average administration times ranged from less than 2 minutes to 6 minutes. Sensitivities and specificities for detecting major depression ranged from 67% to 99% and from 40% to 95%, respectively. No significant differences between instruments were found. Overall sensitivity was 84% (95% CI, 79% to 89%); overall specificity was 72% (CI, 67% to 77%). If a case-finding instrument were administered to 100 primary care patients with a 5% prevalence of major depression, the clinician could expect that 31 patients would screen positive, that 4 of the 31 would have major depression, and that 1 patient with major depression would not be identified. Several instruments with reasonable operating characteristics are available to help primary care clinicians identify patients with major depression. Because the operating characteristics of these instruments are similar, selection of a particular instrument should depend on issues such as feasibility, administration and scoring times, and the instruments' ability to serve additional purposes, such as monitoring severity or response to therapy.