Objectives: To provide evidence for policy makers for human immunodeficiency virus (HIV) prevention and control, we investigated HIV, syphilis, and hepatitis C virus (HCV) infection and the availability of methadone maintenance treatment (MMT) among migrant drug users in Beijing. Methods: A total of 222 participants from 3 main communities where drug abusers reside were interviewed, completed a questionnaire, and were screened for HIV using enzyme-linked immunosorbent assay, confirmed by Western blot. Descriptive statistics, chi(2) tests, and binary logistic regression models were used to analyze differences in HIV and sexually transmitted diseases among different subpopulations. Results: The prevalence of HIV and syphilis in the migrant population was much higher than in permanent residents (43.0% vs 2.1% and 13.3% vs 4.3%, respectively). The HIV-infected cases in the migrant population were 33-fold higher than in permanent residents. Compared with permanent residents, the availability of MMT was much lower in the migrant population (21.9% vs 70.2%), and they were less knowledgeable about MMT (37.0% vs 84.0%). Even for those who were knowledgeable about MMT, methadone treatment was still lower (46.8% vs 82.3%). Compared with the MMT group, higher infection rates of HIV and HCV were found in the no-MMT group (36.7% vs 10.6% and 64.8% vs 50.0%, respectively). Education and employment status contributed to the different distributions between permanent residents and the migrant population and the MMT and no-MMT groups. Conclusions: The prevalence of HIV, syphilis, and HCV infection was higher, and the use of MMT was lower in the migrant population. The migrant population is a noticeable challenge for HIV prevention and control in Beijing.