Pulmonary veno-occlusive disease (PVOD) is currently classified as a type of pulmonary arterial hypertension associated with significant venous or capillary involvement. The classic feature that distinguishes PVOD from other forms of PAH is intimal proliferation and fibrosis of the intrapulmonary veins and venules. PVOD may be idiopathic or associated with infections, genetic factors, toxic exposures, thrombotic diathesis, and autoimmune disorders. Pleural effusions are common.