A good collaboration between health professionals is considered to have benefits for patients, healthcare staff, and organizations. Nevertheless, effective interprofessional collaboration is difficult to achieve. This is particularly true for collaboration between Medical Residents (MRs) and the immediate colleagues they interact with, as Senior Doctors (SDs) and Head Nurses (HNs). Role understanding is one of the factors that may explain difficulties in interprofessional collaboration. Based on this hypothesis, this paper focuses on MRs' role, devoting particular attention to differences in role perception between MRs, SDs, and HNs, and to their consequences for interprofessional collaboration. An exploratory qualitative study inspired by Grounded Theory was conducted in April 2009 in a small peripheral and non-university hospital in Switzerland. Data came from two focus groups with MRs (13), one with SDs (8), and one with HNs (7), and were analyzed using the constant comparative method. Findings show that the expected and the enacted role of MR are perceived differently by SDs, HNs and MRs themselves. To face the inconsistencies within MR's role, the three professional groups develop some adjustments that eventually prove to be paradoxical: on one side, they make collaboration possible and preserve the functioning of the ward, while on the other side they lead to mutual misunderstanding and discontent. These findings suggest that there is an urgent need of defining the role of MRs, of delimiting its boundaries and thereby distinguishing it from other health workers, and eventually of promoting a shared representation of it.