Bronchogenic carcinoma is a cause of parenchymal or hilar masses with or without mediastinal adenopathy in HIV-seropositive smokers. Lung cancer can occur earlier than the more commonly recognized opportunistic infections and in patients not known to be HIV seropositive. Tumor cell types do not differ markedly from those expected in HIV-seronegative young lung cancer patients, but are often poorly differentiated; patients with high-grade malignancies fare poorly independent of their degree of immunocompromise at diagnosis. Computed tomography (CT) scans not only add important information with regard to disease distribution and preferred means of diagnosis, but also result in the detection of new sites of disease with respect to the plain radiography in many patients. Because lung cancer often occurs before the diagnosis of AIDS, the association may not be suspected in some cases; poorly differentiated, rapidly growing tumors in young smokers may raise the suspicion of underlying HIV infection.