In healthcare, organizations increasingly call on clinicians and staff to team up fluidly to deliver integrated services across disciplines and settings. Yet little is known about how clinicians and staff perceive of team membership in healthcare environments where team boundaries are often ambiguous and continually shifting. We draw on the context of primary care in the United States, where fluid multi-disciplinary teamwork is commonly exhorted, to investigate the extent to which clinicians and staff perceive of various roles (e.g., physician, front desk) as members in their teams, and to identify potential implications. Using a survey fielded within 59 clinics (n = 828), we find substantial variation in individuals’ perceptions of the roles they consider as team members during an episode of care (e.g., mean team size = 10.60 roles; standard deviation = 5.09). Perceiving more expansive sets of roles as team members exhibits a positive association with performance as measured by care quality (b = 0.02; p <.01) but a curvilinear association with job satisfaction. Separating an individual’s perceived core (roles always perceived as part of the team) and periphery (roles sometimes perceived as part of the team), perceiving a larger core is positively associated with performance (b = 0.03 p <.01). In contrast, perceiving a larger periphery is marginally negatively associated with performance (b = −0.02, p <.10). This appears to be driven by divergence from the norm perception of the core, i.e., when individuals attribute to the periphery the roles that are considered by most others to be core. Our findings suggest that individuals viewing the roles they must team with more expansively may generate higher quality output but experience a personal toll. Delivering on the ideal of team-based care in dynamic environments may require helping team members gain clarity about their teammates and implementing policies that attend to job satisfaction as team boundaries shift and expand.