Pulmonary capillary hemangiomatosis (PCH) is an extremely rare cause of severe pulmonary hypertension. It is histologically defined by a proliferation of multiple layers of capillaries that expand alveolar septae, and often invade bronchial walls and pleura. The etiology of PCH is currently unknown. Using markers found to be abnormal in samples of the plexiform lesions from patients with idiopathic pulmonary hypertension, we have performed the first detailed immunohistochemical analysis of vascular remodeling in PCH. Like plexiform lesions, the PCH lesion samples have increased expression of markers associated with cellular proliferation and angiogenesis such as vascular endothelial growth factor and Ki-67. In contrast to plexiform lesions, the PCH lesion samples retained markers of cell growth suppression such as peroxisome proliferation-activated receptor-γ and caveolin-1. This confirms that the atypical endothelial cell phenotypes that lead to PCH and idiopathic pulmonary hypertension are distinct.