BACKGROUND: Although shared decision making (SDM) has been reported to facilitate quality care, few studies have explored the extent to which SDM is implemented in primary care and factors that influence its application. This study assesses the extent to which physicians enact SDM behaviors and describes factors associated with physicians' SDM behaviors within the context of depression care. METHODS: In a secondary analysis of data from a randomized experiment, we coded 287 audiorecorded interactions between physicians and standardized patients (SPs) using the Observing Patient Involvement (OPTION) system to assess physician SDM behaviors. We performed a series of generalized linear mixed model analyses to examine physician and patient characteristics associated with SDM behavior. RESULTS: The mean (SD) OPTION score was 11.4 (3.3) of 48 possible points. Older physicians (partial correlation coefficient = -0.29; beta = -0.09; P < .01) and physicians who practiced in a health maintenance organization setting (beta = -1.60; P < .01) performed fewer SDM behaviors. Longer visit duration was associated with more SDM behaviors (partial correlation coefficient = 0.31; beta = 0.08; P < .01). In addition, physicians enacted more SDM behaviors with SPs who made general (beta = 2.46; P < .01) and brand-specific (beta = 2.21; P < .01) medication requests compared with those who made no request. CONCLUSIONS: In the context of new visits for depressive symptoms, primary care physicians performed few SDM behaviors. However, physician SDM behaviors are influenced by practice setting and patient-initiated requests for medication. Additional research is needed to identify interventions that encourage SDM when indicated.