The determinants of study abroad student inflows and outflows are analyzed by comparing the faculties of all Czech public universities. The article develops an institutionalist theoretical perspective that views higher education institutions not only as passive senders and receivers of students but also as active gatekeepers that regulate student flows by balancing the inflows with outflows and vice versa. The theoretical argument is developed against the backdrop of existing theories that emphasize the "push-pull" factors as key determinants of student flows. The argument is tested by regression modeling using an original data set. Inflows are associated with past outflows and vice versa, whereas the importance of push-pull factors is surprisingly small. Important policy implications of these findings as well as implications for theory development are discussed.