BACKGROUND: Depression treatment is often initially sought from primary care physicians. OBJECTIVE: To explore the influence of physician personality on depression assessments. DESIGN: Secondary analysis of data collected in a randomized controlled trial. SETTING: Offices of primary care physicians in Rochester, NY. PARTICIPANTS: Forty-six physicians; six female actors. INTERVENTION: Eighty-six unannounced standardized patient (SPs) visits; physicians saw one SP with major depression and one with adjustment disorder. MEASUREMENTS: SPs listened to audiotapes and completed a form on doctoring behaviors and symptom inquiry immediately following the visit. For the assessment of diagnostic documentation, SPs' medical records were reviewed. Physician personality was assessed via items from the NEO-PI-R. RESULTS: Physicians who are more dutiful and more vulnerable were more likely to document a diagnosis of depression; those who are more dutiful also asked fewer questions concerning mood symptoms. LIMITATION: Roles portrayed by the SPs may not reflect the experience of a typical primary care patient. Most of the PCPs were white men. The sample of PCPs was limited to a single geographic location. Effect sizes were modest. CONCLUSIONS: The clinical, educational, and translational, implications of research showing that physician personality traits could affect practice behaviors warrant consideration. Current models of treatment for depression in primary care could be engineered to accommodate the variability in physician personality. Given that there is no single "correct" way to ask about mood disorders or suicide, clinicians are encouraged to adopt an approach that fits their personal style and preferences.