OBJECTIVE To describe primary care physicians' clinical decision making regarding late-life depression. METHODS Longitudinal collection of data regarding physicians' clinical assessments and the volume and content of patients' ambulatory visits as part of a randomized clinical trial of a physician-targeted intervention to improve the treatment of late-life depression. METHODS Academic primary care group practice. METHODS One-hundred and eleven primary care physicians who completed a structured questionnaire to describe their clinical assessments immediately following their evaluations of 222 elderly patients who had reported symptoms of depression on screening questionnaires. METHODS Intervention physicians were provided with their patient's score on the Hamilton Depression rating scale (HAM-D) and patient-specific treatment recommendations prior to completing the questionnaire regarding their clinical assessment. RESULTS Those physicians not provided HAM-D scores were just as likely to rate their patients as depressed, as determined by specific query of these physicians regarding their clinical assessments. A physician's clinical rating of likely depression did not consistently result in the formulation of treatment intentions or actions. Treatment intentions and actions were facilitated by provision of treatment algorithms, but treatment was received by fewer than half of the patients whom physicians intended to treat. Barriers to treatment appear to include both physician and patient doubts about treatment benefits. CONCLUSIONS Lack of recognition of depressive symptoms did not appear to be the primary barrier to treatment. Recognition of symptoms and access to treatment algorithms did not consistently result in progression to subsequent stages in treatment decision making. More research is needed to determine how patients and physicians weigh the potential risks and benefits of treatment and how accurately they make these judgments.