Pulmonary Kaposi's sarcoma related to the acquired immune deficiency syndrome (AIDS) has not been well characterized. To define the clinical, radiographic, and pathologic features of this entity, 11 autopsy-proved cases of pulmonary Kaposi's sarcoma were reviewed. The most common clinical symptoms were dyspnea and cough, but hemoptysis and stridor were also found. Nodular infiltrates and pleural effusions were the most commonly found radiographic abnormalities. Pulmonary function tests were sensitive in detecting the pulmonary abnormalities due to Kaposi's sarcoma. A low diffusion capacity, lack of arterial desaturation with exercise, and obstruction to airflow were suggestive of pulmonary involvement with this malignancy. Although endobronchial Kaposi's sarcoma was visualized at bronchoscopy as cherry-red, slightly raised lesions, bronchial biopsy specimens always showed no abnormalities. Transbronchial brushings and biopsy specimens and analysis of pleural fluid were also not helpful in establishing a diagnosis. In the seven subjects with extensive parenchymal Kaposi's sarcoma at autopsy, the pleura was always involved. Eight subjects had involvement of the tracheobronchial tree. In all of the subjects, pulmonary Kaposi's sarcoma was a significant cause of morbidity, and in three of 11 subjects (27 percent) it was the direct cause of death.