Pulmonary capillary hemangiomatosis is a rare cause of pulmonary hypertension characterized by extensive proliferation of pulmonary capillaries within alveolar septae. Clinical presentation is nonspecific and includes dyspnea, cough, chest pain, and fatigue. Radiology shows diffuse centrilobular ground-glass opacities. Pulmonary capillary hemangiomatosis is clinically and radiographically indistinguishable from peripheral venoocclusive disease, making microscopic diagnosis essential. Histologically, pulmonary capillary hemangiomatosis shows an abnormal proliferation of small, thin-walled capillaries that expand the alveolar septae. The endothelial cells that comprise these lesions are cytologically bland and show no mitotic activity. Pulmonary capillary hemangiomatosis is important to recognize because prostacyclin therapy, a mainstay in the treatment of pulmonary hypertension, has been reported to cause sudden respiratory distress and death in these patients. Prognosis of this disease remains poor, and the only definitive treatment is lung transplantation.