PURPOSE Most primary care patients have at least 1 major behavioral risk: smoking, risky drinking, low physical activity, or unhealthy diet. We studied the effectiveness of a medical assistant-based program to identify and refer patients with risk behaviors to appropriate interventions. METHODSWe undertook a randomized control trial in a practice-based research network. The trial included 864 adult patients from 6 primary care practices. Medical assistants screened patients for 4 risk behaviors and applied behaviorspecifi c algorithms to link patients with interventions. Primary outcomes were improved risk behaviors on standardized assessments. Secondary outcomes included participation in a behavioral intervention and the program's effect on the medical assistants' workfl ow and job satisfaction.RESULTS Follow-up data were available for 55% of participants at a mean of 12 months. The medical assistant referral arm referred a greater proportion of patients than did usual care (67.4 vs 21.8%; P <.001) but did not achieve a higher success rate for improved behavioral outcomes (21.7 vs 16.9%; P = 0.19). Qualitative interviews found both individual medical assistant and organizational effects on program adoption.CONCLUSION Engaging more primary care team members to address risk behaviors improved referral rates. More extensive medical assistant training, changes in practice culture, and sustained behavioral interventions will be necessary to improve risk behavior outcomes. INTRODUCTIONS moking, risky drinking, physical inactivity, and unhealthy diet are pervasive challenges to health across the world. 1,2 With its high population contact rate, 3,4 primary care is well-positioned to address unhealthy behaviors, but its historical development as a physician-centered acute care delivery system has hampered its ability to manage the large burden of unhealthy behaviors and the chronic diseases that follow. 5 Most practices confront behavioral risks with a very limited response set-physician assessment and management-creating a bottleneck limited by the fl ow of physician workload. 6,7 Better outcomes call for a model of primary care that manages population risk at the necessary scale. 8 Such management requires engaging other members of the primary care team and forging linkages with community resources that can amplify the practice's impact. 9 A framework for managing behavioral risks in primary care emerges from the concept of multiscale complexity. 10 Organizations that address complicated problems must perform an array of tasks that vary in complexity and scale. Complexity measures the degree to which tasks require independent judgment and customization to produce a good outcome. Scale quantifi es the number of tasks to be performed. An important principle in optimizing effi ciency, therefore, is to correctly design a system that can respond to its environment with both low-variety and low-complexity tasks delivered on a 505 PRO GR A M TO PRO M OT E HE A LT HY BEHAV IOR Slarge scale, and high-variety and hig...