The erythropoietic system plays a major role in tissue oxygenation because the erythrocytes are the primary carriers of oxygen in the form of oxyhemoglobin. Therefore, clinical entities such as abnormal hemoglobins, polycythemia, anemia, and significant changes in blood volume frequently produce alterations in various respiratory functions. The pulmonary manifestations can vary from mild respiratory illness to life-threatening emergencies with high mortality rates. Among the hemoglobinopathies, sickle cell disease is clinically the most important and commonly associated with serious pulmonary consequences, including acute chest syndrome, pneumonia, infarction due to in situ thrombosis, bone marrow fat embolism of pulmonary vasculature, bone marrow infarction, pulmonary hypertension, and other abnormalities. Hemoglobinopathies with high and low affinity for oxygen and other abnormal hemoglobinopathies occasionally cause clinically significant respiratory complications by interfering with normal tissue oxygenation. Acquired methemoglobinemia can cause alarming cyanosis and medical emergency. Erythrocyte disorders are associated with pulmonary complications, including pulmonary hypertension, alveolar fibrosis, and pulmonary dysfunction. Coagulation disorders, both the inherited and acquired types, have the potential to affect the respiratory system in the form of hemorrhage from the airways, lung parenchyma, or pulmonary hypertension. The following paragraphs describe the common pulmonary complications and manifestations associated with hemoglobinopathies, erythrocyte disorders, and coagulation abnormalities.