Acute pulmonary complications of sickle cell anemia are sickle cell lung disease and bacterial pneumonias. Chronic abnormalities in lung function include a restrictive ventilatory defect and perhaps increased venous admixture to the pulmonary circulation. Coexisting sarcoidosis may complicate sickle cell anemia and interact to potentiate sickling. Sickle cell lung disease, or acute "chest syndrome," occurs with greatest frequency in adults, is due primarily to pulmonary infarction, and may lead to cor pulmonale. On the other hand, bacterial pneumonia due to Streptococcus pneumoniae occurs with greater frequency in infancy and childhood. Mycoplasma and other organisms may also cause pneumonia with protracted illness and slow resolution. Bacteremia and meningitis may be further complications, particularly in children. Precise diagnosis of the acute febrile pulmonary episode is often difficult. In adults the illness is commonly self-limited. However, a vigorous diagnostic approach is warranted in all severely ill patients.