Studies of alcohol use in HIV-1 infected patients have resulted in conflicting and limited information regarding prevalence, as well as impact on HIV replication, disease progression and response to antiretroviral therapy. Alcohol, drug abuse and past medical information, including antiretroviral treatment, were obtained using research questionnaires and medical chart review in 220 HIV-1 infected drug users. A physical examination was conducted and blood was drawn to evaluate immune measures and nutritional status. Heavy alcohol consumption, defined as daily or 3-4 times per/week, was reported in 63% of the cohort. Men (odds ratio (OR)=2.6, 95% CI 1.13-5.99, p =0.013), and participants between 35 and 45 years of age were three times more likely to be heavy alcohol users (p =0.006 and 0.0009, respectively). Low serum albumin levels were more evident in heavy alcohol users than non-drinkers (p =0.003). Heavy alcohol users receiving antiretroviral therapy were twice as likely to have CD4 counts below 500 than light or non-drinkers (95% CI, 1-5.5, p =0.03), and highly active antiretroviral therapy (HAART)-treated heavy alcohol users were four times less likely to achieve a positive virological response (95% CI, 1.2-17, p =0.04). Alcohol consumption is prevalent in our HIV-1 infected drug user cohort and significantly impacts both immunological and virological response to HAART treatment.