The increased risk of developing lung diseases in cigarette smokers has been well recognized. The association between smoking and the risk of developing pulmonary infections in HIV-1-infected patients, however, which has not been established, was evaluated in the present study. Twenty-seven cases with lower respiratory infections (15 Pneumocystis carinii pneumonia (PCP), 12 TB cases) were compared with 27 age, gender, socio-economic and HIV status-matched patients, without history of respiratory diseases. Medical history and physical examinations were obtained every 6 months. Blood was drawn for CD4 and viral load measurements. A substantial number of HIV + smokers who developed PCP (one-third) had been on highly active retroviral therapy (HAART) for more than 6 months and prophylaxis had been discontinued. Multivariate analyses indicated that in HIV-infected people, after controlling for HIV status and antiretrovirals, cigarette smoking doubled the risk for developing PCP (p = 0.01). Multivariate analyses demonstrated that long-term smoking also increased the risk (2 x) of developing tuberculosis (p = 0.04). Moreover, daily tobacco use seemed to attenuate by 40% the immune and virological response to antiretroviral therapies. These findings indicate that tobacco use significantly increases the risk of pulmonary diseases in HIV infected subjects and has a potential deleterious impact on antiretroviral treatment.