Injection drug use (IDU) and HIV infection are important public health problems in Vietnam. The IDU population increased 70% from 2000 to 2004 and is disproportionately affected by HIV and AIDS -- the country's second leading cause of death. Hepatitis B virus (HBV) and hepatitis C virus (HCV) share transmission routes with HIV and cause serious medical consequences. This study aimed to determine risk factors for acquisition of HIV, HBV, and HCV infections among IDUs in a northern province. We conducted a matched case-control study among active IDUs aged 18-45 who participated in a community-based survey (30-minute interview and serologic testing). Each HIV-infected IDU (case) was matched with one HIV-uninfected IDU (control) by age, sex (males only), and study site (128 pairs). Similar procedures were used for HBV infection (50 pairs) and HCV infection (65 pairs). Conditional logistic regression models were fit to identify risk factors for each infection. Among 309 surveyed IDUs, the HIV, HBV, and HCV prevalence was 42.4%, 80.9%, and 74.1%, respectively. Only 11.0% reported having been vaccinated against hepatitis B. While 13.3% of the IDUs reported sharing needles (past six months), 63.8% engaged in indirect sharing practices (past six months), including sharing drug solutions, containers, rinse water, and frontloading drugs. In multivariable models, sharing drugs through frontloading was significantly associated with HIV infection (odds ratio [OR]=2.8), HBV infection (OR=3.8), and HCV infection (OR=4.6). We report an unrecognized association between sharing drugs through frontloading and higher rates of HIV, HBV and HCV infections among male IDUs in Vietnam. This finding may have important implications for bloodborne viral prevention for IDUs in Vietnam.