Migration is one social factor responsible for the spread of HIV/AIDS. The objectives of this project were to describe migration patterns, including rates of and types of migration, among participants in the Vancouver Injection Drug Users Study (VIDUS); to identify factors associated with migration; and to determine the impact of migrating out of Greater Vancouver (GV) on drug use practices and HIV-related risk behaviours among this population. Methods: VIDUS is an open prospective cohort of

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... ection drug users (IDU). At baseline and semi-annually, participants complete an interviewer-administered questionnaire which elicits socio-demographic data, information regarding injection and non-injection drug use, sexual risk behaviours and enrollment into addiction treatment. A l l participants were residents of GV at the time of recruitment. Correlates of migration, defined as living outside GV during follow-up, were first identified for all participants with at least one follow-up between June 1999 - May 2005. In a separate analysis, risk behaviours were compared before and after a move had occurred for all eligible participants with more than one follow-up between May 1996 - November 2005. Results: A total of 1603 IDU were recruited between May 1996 and November 2005. 1245 participants had at least one follow-up between June 1999 and May 2005. The proportion of I DU living outside of GV during follow-up ranged between 2.5% and 11.8% and a total of 149 locations where participants migrated to were cited, with the majority (53.7%) being within British Columbia. Migrating was negatively associated with various factors including frequent crack and heroin use, sex trade involvement, and current methadone use. Of 1122 participants with more than one follow-up visit between May 1996 and November 2005,192 (17%) reported migrating out of GV while 930 (83%) participants did not report such a move and movers were significantly younger. A significant decrease in frequent heroin and frequent [...]