Pregnancy induces significant physiologic stresses on the pulmonary and cardiovascular systems that may precipitate respiratory compromise. In addition, certain disease states that are unique to the pregnant woman, such as amniotic fluid emboli syndrome, may be associated with respiratory failure. The physiologic changes that affect the pregnant woman are reviewed. Pregnancy-related conditions are discussed as well as how common diseases, such as the acute respiratory distress syndrome, asthma, pneumonia, and AIDS,have to be approached when balancing the needs of the fetus with maternal well-being.