Background From 2014 to 17, a large-scale project, ‘The User-involving Hospital’, was implemented at a Danish university hospital. Research highlights leadership as crucial for the outcome of change processes in general and for implementation processes in particular. According to the theory on organizational learning by Agyris and Schön, successful change requires organizational learning. Argyris and Schön consider that the assumptions of involved participants play an important role in organizational learning and processes. The purpose was to explore leaders’ assumptions concerning implementation of patient involvement methods in a hospital setting. Methods Qualitative explorative interview study with the six top leaders in the implementation project. The semi-structured interviews were conducted and analyzed in accordance with Kvale and Brinkmanns’ seven stages of interview research. Result The main leadership assumptions on what is needed in the implementation process are in line with the perceived elements in organizational learning according to the theory of Argyris and Schön. Hence, they argued that implementation of patient involvement requires a culture change among health care professionals. Two aspects on how to obtain success in the implementation process were identified based on leadership assumptions: “The health care professionals’ roles in the implementation process” and “The leaders’ own roles in the implementation process”. Conclusion The top leaders considered implementation of patient involvement a change process that necessitates a change in culture with health care professionals as crucial actors. Furthermore, the top leaders considered themselves important facilitators of this implementation process.