Incidence and mortality of AIDS patients have significantly declined in the developed countries due to the very active anti-HIV combination therapy available today. Because of the prolongation of the survival expectancy of these patients, other non-AIDS defining tumours have been recently reported in several cohort studies with increased frequency. We want to report the clinico-pathological features and the outcome of 39 patients with lung cancer and HIV infection, collected by the Italian Cooperative Group on AIDS and Tumors (GICAT) between 1986 and December 1997. As a control group, we decided to evaluate patients, less than 60 years of age, with lung cancer but without HIV infection seen at the CRO, Aviano, during 1995 and 1996. The median age of the study group patients was 38 years (range 28-58) and 90% of them were males. Sixty-nine percent of patients were intravenous drug users and HIV infection was asymtomatic in 41% of patients. NSCLC was observed in 78% of patients, SCLC in 13% and mesothelioma in 8%. Among NSCLC, adenocarcinoma was the most frequently observed histological subtype (48%). No differences were found as regards the stage of disease at diagnosis and the histologic subtype in comparison with the control group. The median overall survival was significantly shorter for patients with HIV infection when compared to that of the control group (5 months vs. 10 months, P < 0.0001). In conclusion, the outcome of patients with SNCLC and HIV infection seems worse than that of the general population, suggesting a synergistic and/or addictive adverse effect of HIV on the outcome of lung cancer.