Contributions on interdisciplinary research have so far focused on barriers to such collaborations and strategies for overcoming these. In this paper, we propose that a geographical perspective contributes to understand the formation of successful interdisciplinary research collaborations. The empirical analysis of a centre for clinical cancer research illustrates the importance of considering the role of geographical proximity to collaborators and decision-makers, as well as the co-location of excellent research groups within different fields, in overcoming barriers to interdisciplinary research. We suggest that policies aimed at stimulating lasting interdisciplinary research collaborations should take the distance between collaborators into account.