We describe the first cases of familial pulmonary capillary hemangiomatosis, a disorder in which capillaries in the lungs proliferate. Three siblings died from primary pulmonary hypertension. One developed pulmonary congestion preterminally after vasodilator treatment. The inheritance pattern seems autosomal recessive. Lung specimens obtained in two siblings showed extensive pulmonary capillary hemangiomatosis, with normal capillaries proliferating into veins and alveoli. Including our patients, four of the nine patients with pulmonary capillary hemangiomatosis have presented with the clinical picture of primary pulmonary hypertension. Thus, pulmonary capillary hemangiomatosis should be considered as a histologic pattern of primary pulmonary hypertension. Most other cases of pulmonary capillary hemangiomatosis have been similar to pulmonary veno-occlusive disease. Recently, disorders involving the proliferation of cytologically normal capillaries have been termed angiogenic diseases. Pulmonary capillary hemangiomatosis may be an angiogenic disease.