Dissecting aneurysm of the aorta is often seen; similar changes in the pulmonary artery are rare. In the German literature they are unknown. 11 previously described cases have been compiled with their clinical and pathological records, and a new added. The patient, a 45 year old woman, suffered from pulmonary hypertension which resulted in medionecrosis and a large aneurysm of the trunk of the pulmonary artery. She died of haemopericardium after rupture of the artery in two stages, with a tear of 8 cm in the trunk which reached to the bifurcation of the vessel.