We report from a multi-level study investigating the diffusion of robotic surgery in the Italian health care system between 1999 and 2010. A combination of qualitative and quantitative methods allowed us to link organization-level processes associated with the adoption and implementation of the innovation with its diffusion at population level. Our findings advance our understanding of how early implementations influence later adoptions, by drawing attention to how the search for social gains pushes some peripheral actors to pioneer an innovation, and to engage in practices of dissemination of their experience that constitute these actors as "exemplary users." These practices eventually trigger and support diffusion even in the presence of persisting uncertainty about the technical and economic benefits of the innovation.