An interesting case of fibrosing mediastinitis, which is a rare cause of total nonvisualization of one lung on pulmonary scintigraphy, is presented. Scintigraphy with Tc-99m MAA showed a severe deficit of perfusion in the right lung, with normal perfusion of the left lung. Ventilation images were normal. CT and MRI each demonstrated the mediastinal nodal enlargement and MRI demonstrated the "flow void" signal phenomenon in the right pulmonary artery indicating its patency. Confirmation of actual patency without pulmonary artery emboli and with poor venous opacification was documented with angiography. Multiple complementary imaging modalities were helpful in correctly diagnosing fibrosing mediastinitis from an extensive list of differential possibilities for unilateral non-visualization of the lung on perfusion scanning.