Purpose Although some evidence suggests that resident duty hours reforms can lead to shift-worker mentality and loss of patient ownership, other evidence links long hours and fatigue to poor work performance and loss of empathy, suggesting the restrictions could positively affect professionalism. The authors explored perceived impacts of a 16-hour duty restriction, achieved using a night float (NF) system, on the workplace and professionalism. Method In 2013, the authors conducted semistructured interviews with 18 residents, 9 staff physicians, and 3 residency program directors in the McGill University core internal medicine residency program regarding their perceptions of the program's 12-hour shift-based NF system. Interviews were transcribed and coded for common themes. The authors used a descriptive qualitative methodology. Results Participants viewed implementation of the NF system as leading to decreased physical and mental exhaustion, more consistent interaction with patients, and more stable team structure within shifts compared with the previous 24-hour call system. These workplace changes were felt to improve teamwork and patient ownership within shifts, quality of work performed, and empathy. Across shifts, however, more frequent sign-overs, stricter application of shift time boundaries, and loose integration between daytime and NF teams were perceived as leading to emergence of shift-worker mentality around sign-over. Perceptions of optimal patient ownership changed from the traditional single-physician-24/7 model to team-based shared ownership. Conclusions Duty hours restrictions, as exemplified by an NF system, have both positive and negative impacts on professionalism. Interventions and training toward effective team-based care are needed to curb emergence of shift-worker mentality.