Prior reports of an increased risk of lung cancer in HIV-infected individuals have not always included control groups, nor considered other risk factors such as tobacco exposure. We sought to determine the role of HIV infection and highly active antiretroviral therapy (HAART) on lung cancer incidence in 2,651 HIV-infected and 898 HIV-uninfected women from the Women's Interagency HIV Study (WIHS). A prospective study of the incidence rates of lung cancer was conducted, with cases identified through medical records, death certificates, and state cancer registries. Standardized incidence ratios (SIRs) were calculated to compare lung cancer incidence among HIV-infected and uninfected WIHS participants, with population-based expectations using the Surveillance, Epidemiology, and End Results registry. Behavioral characteristics in the WIHS were compared to US women by age and race adjusting the population-based data from the National Health and Nutritional Examination Survey (NHANES) III. Incidence rates of lung cancer were similar among HIV-infected and uninfected WIHS women. Lung cancer SIRs were increased in both HIV-infected and -uninfected women compared with population expectations, but did not differ by HIV status. Among HIV-infected women, lung cancer incidence rates were similar in pre-HAART and HAART eras. All WIHS women with lung cancer were smokers; the risk of lung cancer increased with cumulative tobacco exposure. WIHS women were statistically more likely to smoke than US women studied in NHANES III. HIV infection is strongly associated with smoking behaviors that increase lung cancer risk. The role of HIV itself remains to be clarified.