Several types of neoplastic conditions are included in the differential diagnosis of pneumonia. Bronchial obstruction with cancer can produce obstructive pneumonia that results in intractable infection. Bronchogenic carcinoma and metastatic cancer involving the airways may produce this clinical presentation. Bronchioloalveolar carcinoma is a relatively common form of primary lung cancer that characteristically presents as a chronic infiltrate associated with cough, hypoxemia, shortness of breath, and mucus hypersecretion. This cancer has two distinct histological types with markedly different prognosis. The mucinous variety is much more likely to be multicentric and rapidly progressive whereas the nonmucinous variety may be localized. Lymphoproliferative diseases may also present in an infiltrative appearance. Kaposi's sarcoma infiltrating the lungs, particularly associated with acquired immune deficiency syndrome, presents a diagnostic dilemma because of the high incidence of pulmonary infection in these patients.