The authors report the case of a 56-year old woman who had presented with clinical symptoms resembling those of pulmonary embolism and due to chronic dissection of the first aortic segment compressing the right branch of the pulmonary artery. Eighteen months after the acute episode, the diagnosis was suspected at echocardiography, but the other paraclinical examinations performed (scintigraphy of the lung, angiography, computerized tomography) failed to display the aortic dissection, although they enabled the diagnosis to be approached and the physiopathology to be determined. At surgery, a type II dissection was discovered, the compression was relieved and the pulmonary artery was recanalized. The post-operative period was uneventful, with return to normal of the scintigraphic and CT images. This case is exceptional in that it is extremely rare (this is the 6 th case reported) and the lesion was well tolerated, probably due to the presence of a systemic-pulmonary circulation.