We report a case of pulmonary artery dissection imaged by MR. Dissection of a markedly dilated pulmonary artery is a rare and usually fatal complication of chronic pulmonary arterial hypertension. The diagnosis is made at autopsy, with only two cases having previously been documented (by Doppler echocardiography) during life. The hallmark of an arterial dissection is the finding of an intimal flap and a false lumen. In our case, spin echo MR imaging failed to show either the intimal flap or any intraluminal signal defects. The dissection was presumably obscured by nonhomogeneous intraluminal signal caused by the slow blood flow associated with severe pulmonary arterial hypertension. Cine MR imaging, however, demonstrated different signal intensity within the true and false lumens of the dissection, thereby outlining the intimal flap between the two channels.