Chronic pulmonary thromboembolism plays an important role in cardiac failure which is a major cause of death in thalassemic patients over 20 years of age. This report is a study of autopsy lung tissue from 58 patients with beta-thalassemia/hemoglobin E disease (beta-thal/HbE), including whole lungs from five, 13 patients with hemoglobin H disease (HbH), and eight patients with beta-thalassemia major (beta-thal) including whole lung from one. Pulmonary thromboembolic lesions were found in 24 of 58 (41%) patients with beta-thal/HbE, of which 21 of 39 (54%) were splenectomized patients and 3 of 19 (16%) were nonsplenectomized patients, with the incidence increasing with age. Lung maps showed the greatest number of lesions in the lingula, right middle lobe, and anterior segments of both upper lobes. Pulmonary thromboembolic lesions were also found in one of 13 HbH patients and one of 8 beta-thal patients, both splenectomized. Eight of the 27 patients with these lesions had right ventricular and 14 biventricular hypertrophy, reflecting the deleterious effect of such lesions. Possible causative factors are discussed.