We develop and test a model of the effects of transformational leadership beyond the boundaries of a team to the level of collaboration with other teams. We also test team size as a boundary condition in this relationship. In a study using a crisscross design to control common method bias, using a sample of 388 teams from a leading, global electronics company, the results from structural equation modeling (SEM) reveal that teams with transformational leaders are more likely to have higher internal teamwork quality (TWQ) and receive high inter-team collaboration ratings from other teams. Results further support the expectation that the association between transformational leadership and inter-team collaboration is mediated by TWQ and moderated by team size. The importance of transformational leadership for team-level research, as well as its hidden benefits beyond internal team boundaries, is discussed.