Objective: To determine whether observed patterns of physician interaction around shared patients are associated with higher levels of teamwork as perceived by physicians. Data Sources/Study Setting: Michigan Medicare beneficiaries who underwent coronary artery bypass grafting (CABG) procedures at 24 hospitals in the state between 2008 and 2011. Study Design: We assessed hospital teamwork using the teamwork climate scale in the Safety Attitudes Questionnaire. After aggregating across CABG discharges at these hospitals, we mapped the physician referral networks (including both surgeons and nonsurgeons) that served them and measured three network properties: (1) reinforcement, (2) clustering, and (3) density. We then used multilevel regression models to identify associations between network properties and teamwork at the hospitals on which the networks were anchored. Principal Findings: In hospitals where physicians repeatedly cared for patients with the same colleagues, physicians perceived better teamwork (Î²-reinforcementÂ =Â 3.28, pÂ =Â .003). When physicians who worked together also had other colleagues in common, the reported teamwork was stronger (Î² clusteringÂ =Â 1.71, pÂ =Â .001). Reported teamwork did not change when physicians worked with a higher proportion of other physicians at the hospital (Î² densityÂ =Â âˆ'0.58, pÂ =Â .64). Conclusion: In networks with higher levels of reinforcement and clustering, physicians perceive stronger teamwork, perhaps because the strong ties between them create a shared understanding; however, sharing patients with more physicians overall (i.e., density) did not lead to stronger teamwork. Clinical and organizational leaders may consider designing the structure of clinical teams to increase interactions with known colleagues and repeated interactions between providers.