BACKGROUND: Little is known about processes by which proactive primary care teams might activate their patients. We examine the role of trust in patient-physician relationships for translating practice teamwork into patient activation. METHODS: Data were collected by surveys of adult enrollees and primary care teams of a group-model managed care organization in metropolitan Atlanta. Enrollees who were 25-59 years of age were randomly sampled from 3 condition cohorts (diabetes, elevated lipids but no coronary artery disease history, and low risk). A total of 2224 responded to a mixed mode survey in 2005 (42% response rate). Ninety-seven practitioners and 187 support staff of 16 primary care teams responded to a practice climate survey in 2004 (85% response rate). Practice climate is a multidimensional concept measuring support and collaboration with a team. Linear models of patients nested within their primary care teams were estimated for patient trust in physician as a function of practice climate and for activation as a function of trust, adjusted for other respondent characteristics. RESULTS: We found significant, positive associations between practice climate and patient trust in their primary care physicians and between patient trust and activation in their health. CONCLUSIONS: Our study shows 1 process by which practice climate translates into patient activation. Supportive interactions among practitioners and staff within primary care teams facilitate trust-building interactions between practitioners and patients. Supportive, trustworthy interactions, in turn, help to ameliorate the inherent imbalance in power between patients and physicians, contributing to patients who take a more active role in their health.