We present a rare case of aortitis syndrome associated with dilatation of aorta and coarctation-like effect due to the intraluminal flap formation originated from dissected wall of the aorta. A 31-year-old woman was admitted to our hospital complaining of shortness of breath, palpitation and cough. On admission, her physical status showed congestive heart failure and hypertension of upper extremities and hypotension of lower extremities. Bruits were audible over the neck, the anterior chest and the back. Serological studies showed active inflammation. Chest X-ray film showed upper mediastinal widening, cardiomegaly and pulmonary edema. Aortitis syndrome was strongly suggested by these clinical findings, so that prednisolone therapy was started on 3rd hospital day. Special examinations were performed several days later when inflammatory changes showed a tendency to improve. Chest CT scan, RI angiography and MRI studies showed an aneurysmal dilatation from the ascending aorta to the mid-thoracic aorta. Aortography demonstrated a flap at the terminal portion of this aneurysmal dilatation and grade II (Sellars) aortic regurgitation. There was a pressure difference of 80 mmHg between the parts abutting cranial and caudal sides of the flap. A surgical operation was, then, performed to correct the pressure difference. The dissected wall was extruded toward the aortic lumen creating a flap (2 cm in length). This flap was resected and an artificial graft was inserted. Histologically, the flap consisted of adventitia, media and intima.(ABSTRACT TRUNCATED AT 250 WORDS)