Back-and-forth enrollment at different institutions--student swirl--and concurrent enrollment at two or more institutions--double-dipping--have become common experiences for students in the United States. However, empirical studies explaining student mobility are rather rare. This study examines how student departures from and returns to a single institution are affected by college attendance elsewhere. The model presented here demonstrates that departure rates are higher for students concurrently attending another college. Return rates, on the other hand, are substantially lower for those students who attend other colleges after departure from the study institution. The effect of multi-institutional attendance differs by college type, with the effect of four-year out-of-state institution attendance being most pronounced. The simultaneous analysis of departures and returns provides the study institution with a more accurate and complete picture of student mobility. (Contains 5 tables and 5 figures.)