Despite much interest in plexiform lesions, no published work compares their distribution in different types of pulmonary hypertension. Scattered reports of plexiform lesions in bronchial arteries oppose the consensus view that the lesions develop in pulmonary arteries. To compare the localization of plexiform lesions in different types of pulmonary hypertension, and to assess the role of the bronchial arteries in their formation, we examined by light microscopy lung tissue from five patients with primary plexogenic pulmonary arteriopathy (PPPA), six with pulmonary hypertension secondary to congenital cardiac malformations (CCM), and one with pulmonary hypertension complicating hepatic cirrhosis. We classified the 270 plexiform lesions observed as either preacinar or intra-acinar based on the type of pulmonary artery in which they were located, and computed the frequencies of each type of lesion within each etiologic group. We searched for lesions developing in bronchial arteries. Then, postulating that a close anatomic relationship between plexiform lesions and bronchial arteries would necessitate a clustering of the lesions near sites in the lung subserved by the bronchial circulation, we measured, for 211 of the 270 lesions previously classified, the distance from the lesion to the nearest airway and computed the mean lesion-to-airway distance in each etiologic group. The frequencies of preacinar plexiform lesions were 34% in PPPA, 67% in CCM (P < .01), and 21% in the case of cirrhosis. We found no plexiform lesions within bronchial arteries, and the mean plexiform lesion-to-airway distances were 1,680 +/- 180 microns in PPPA, 1,330 +/- 220 microns in CCM, and 2,050 +/- 1,090 microns in cirrhosis (P > .05). Our data suggest that (1) the distribution of plexiform lesions within the pulmonary arterial tree varies depending on the etiology, (2) plexiform lesions rarely if ever arise in bronchial arteries, and (3) plexiform lesions are not preferentially distributed near parts of the lung subserved by the bronchial circulation.