Previous studies of medical outpatients have documented a high prevalence of depression that is often unrecognized by primary physicians. However, the subjective methodologies of most of these studies limit their quantitative and comparative usefulness. By contrast, in the present study, 526 medical outpatients completed a self-report questionnaire, the Beck Depression Inventory (BDI). Questionnaire results were calibrated by psychiatric interviews of a subsample of 41 patients. The prevalence of depression was 12.2% when at least mild depression was used as a criterion; the rate for moderate depression was 5.5%, and the rate for severe, probably "psychotic," depression was 0.6%. A review of medical charts showed that primary physicians failed to diagnose about 50% of both depressed and otherwise impaired patients. The BDI was shown to be a sensitive screening test; its use is advocated to improve recognition of depression by primary physicians.