Pulmonary arterial hypertension has many causes, only some of which are well understood. The radiographic findings in pulmonary arterial hypertension are very similar regardless of the cause. Some radiographic features such as cardiac chamber enlargement, occur secondary to elevation of pulmonary pressures. In addition, sequential radiographs may demonstrate dramatic changes as the hypertension develops. This article presents examples of the various forms of pulmonary arterial hypertension, with pathologic correlation. Included are chronic pulmonary thromboembolism, plexogenic pulmonary arteriopathy, pulmonary venooclusive disease and persistent fetal circulation. Examples of lesions causing secondary pulmonary arterial hypertension: parenchymal lung disease, pulmonary venous hypertension, and congenital heart disease, are also illustrated.