Pulmonary veno-occlusive disease is a rare disorder characterized by an obliterative fibrosing venulitis. The etiology and pathogenesis of this disease is not well understood. This case is one secondary to granulomatous venulitis. Ultrastructural study demonstrated reduplication of capillary basal laminae, endothelial swelling, and granuloma formation, but shed no light on the etiology of the disease. The formation of noncaseating granulomas involving only intralobular veins is most unusual and has not been previously described in pulmonary veno-occlusive disease.