Vascular lesions in lungs of patients with pulmonary arterial hypertension (PAH) (Group 1 in the WHO updated clinical classification, 2013) occur mainly in pre- and intra-acinar muscular arteries less than 500 μm in diameter and are characterized by variable existence of constrictive (occlusive) lesions and advanced complex lesions (i.e. plexiform lesions, dilatation lesions, and vasculitis). On the other hand, the rare entities of pulmonary veno-occlusive disease (PVOD) and pulmonary capillary hemangiomatosis (PCH) involve mainly veins/venules and capillaries, respectively. The fibrotic occlusive changes in pulmonary veins and venules in PVOD can lead to capillary engorgement and even capillary proliferation, often mimicking PCH (PCH-like lesion). The histological and clinical similarities have raised questions about a possible overlap between PVOD and PCH. Therefore both diseases are now classified together as a single subcategory (group 1´). Because of the postcapillary block, caution should be taken with the use of vasodilators. Here we will briefly describe the histopathology of PAH and PVOD/PCH with recent observations.