The aim of this study was to explore differences between primary care and tertiary psychiatry patients meeting DSM-III-R criteria for depressive disorders in terms of a wide range of demographic and clinical variables including psychiatric comorbidity. A weighted sample of 153 depressed primary care patients was obtained from the waiting rooms of family physicians using a two-stage selection and assessment procedure including the Structured Clinical Interview for the DSM-III-R (SCID). A measure of physician detection was also obtained. The 123 depressed psychiatric patients were seeking evaluation and treatment at a university-based depression program, and DSM-III-R diagnoses were also obtained using the SCID. Overall, fewer depressed primary care patients met criteria for major depressive disorder, and more of those who did were only midly depressed. Depressed primary care patients were more likely to be women, older, and had less education, less past treatment, and greater lifetime comorbidity. Clinical differences were greatest for the depressed patients who had gone undetected by their physicians: they were higher functioning, less distressed, and more mildly depressed. Findings are discussed in terms of the validity and acceptability of practice guidelines for depression in primary care.