To investigate prevalence of human immunodeficiency virus (HIV) infection and risk factors for its transmission among injection drug users (IDUs) in Liangshan Yizu Autonomous Prefecture of Sichuan Province, China. A community-based survey was conducted to investigate demographic characteristics, pattern and frequency of sharing injection equipment, and sexual behaviors in IDUs. Blood samples were also collected from them to detect for antibodies against HIV and syphilis. A total of 379 subjects were recruited with informed consent for study through community outreach and peer recruiting methods. Their prevalence of HIV infection was 11.3% (43/379). Ethnicity, frequency of sharing syringes and cotton swab during the past three months and syphilis infection associated with HIV infection by univariate analysis using chi-square test. Multivariate logistic regression analysis showed odds ratio of frequency of sharing syringes for HIV infection during the past three months was 2.28 (95% CI 1.18 - 4.43), and that for syphilis infection 3.10 (95% CI 1.48 - 6.48). Frequency of sharing syringes during the past three months associated with syphilis and HIV infection.