Purpose: The purpose of the study is to determine whether one leader set-up is better than the others according to interdisciplinary cooperation and leader legitimacy. Design/methodology/approach: The study is a qualitative study based on semi-structured interviews at three Danish hospitals. Findings: The study found that the leadership set-up did not have any clear influence on interdisciplinary cooperation, as all wards had a high degree of interdisciplinary cooperation independent of which leadership set-up they had. Instead, the authors found a relation between leadership set-up and leader legitimacy. In cases where staff only referred to a leader from their own profession, that leader had legitimacy within the staff group. When there were two leaders from different professions, they only had legitimacy within the staff group from their own profession. Furthermore, clinical specialty also could influence legitimacy. Originality/value: The study shows that leadership set-up is not the predominant factor that creates interdisciplinary cooperation; but rather, leader legitimacy also should be considered. Additionally, the study shows that leader legitimacy can be difficult to establish and that it cannot be taken for granted. This is something chief executive officers should bear in mind when they plan and implement new leadership structures. Therefore, it would also be useful to look more closely at how to achieve legitimacy in cases where the leader is from a different profession to the staff.