摘要Objective:To determine the prevalence of HIV infection among homeless men and women and the related risk behaviors in Tehran, Iran. <br> Methods: In 2007-2008, Tehran municipality stacked up 10 657 homeless men and women for assessment of HIV and began collaboration with Iranian Research Center for HIV/AIDS (IRCHA) departments to conduct HIV infection prevalence surveys in homeless populations. The results were analyzed for associations with demographic information, family support, status of drug abuse and relation with family and friends. <br> Results:Overall HIV prevalence was 1.7%(95%confidence interval 1.4-1.9). Factors independently associated with HIV infection included history of using drugs [AOR 8.15 (4.86-13.67)], older age [AOR 1.80 (1.08-2.99) for 40- 55 yr], occupation [AOR 1.64 (1.19-2.24) for unemployed], and no relation with family [AOR 1.82 (1.30-2.54)]. <br> Conclusions: This study supports the idea that injection drug use is contributing to the increased spread of HIV among Iranian homeless. Harm reduction programs should be expanded, particularly among homeless injection drug users.