This study examined mobility on the airbridge between New York (NY) and Puerto Rico (PR) for Puerto Rican drug users and its relationship to HIV risk. Over 1,200 Puerto Rican injection drug users (IDUs) and crack smokers were recruited by outreach workers in NY and PR; interview data included questions on mobility (lifetime residences and recent trips). Two-thirds of the NY sample had lived in PR; one-quarter of the PR sample had lived in NY; the most commonly sited reasons for moving were family-related. Fewer than 10% had visited the other location in the prior 3 years. Variables related to risk were number of moves, recent travel, and having used drugs in PR (all with p < 0.05). Implications included the need to enhance risk reduction efforts for IDUs in PR and address sexual risk among mobile drug users.