To determine demographic and behavioral factors associated with client-reported HIV infection among new enrollees in methadone maintenance treatment programs (MMTPs) in Massachusetts and Connecticut, we examined ethnographic data and interview data from MMTP clients (N = 674). Clients responded to questions about behaviors in the 30 days before drug treatment. ETHNOGRAPH was used to analyze qualitative data, and logistic regression analysis was used to identify variables associated with client-reported HIV infection. Statistical significance was set at p < .05. The client-reported HIV infection rate was 20% (132/674). Odds ratios for factors associated with client-reported HIV infection were being white (0.53), increase in age (1.07), use of non-injected heroin (0.12), use of injected heroin (6.24), cocaine injection (1.78), sharing of "works" with strangers (2.15), and "safer sex" behavior (4.04). Additionally, 35% of those who did not use illicit drugs reported being seropositive. The qualitative data suggested HIV positive clients were concerned about protecting sex partners, and learning of HIV infection motivated some to stop using drugs. Although some clients engaged in low-risk behaviors, others did not, therefore the potential for HIV transmission among injection drug users (IDUs) in Connecticut and Massachusetts exists. HIV prevention and drug treatment program personnel should reinforce and build on the low-risk behaviors that are acceptable and adopted by some in this population.