A 30-year-old man suffered from transient left hemiparesis and was admitted under the clinical diagnosis of transient ischemic attack. Cerebral angiogram on admission disclosed severe stenosis at the horizontal portion of the right middle cerebral artery. Magnetic resonance images (MRI) on axial view showed a linear enhanced lesion along the stenosis. Images on sagittal view disclosed a crescent-like lesion surrounding a flow void of the middle cerebral artery. After administration of aspirin, he had never suffered from hemiparesis. The enhanced lesion of the middle cerebral artery gradually disappeared on MRI. Although the middle cerebral artery showed temporary improvement of the stenotic lesion, it finally occluded 9 months after the onset. A diagnosis of spontaneous dissection of the right middle cerebral artery was made. The process of the arterial hemodynamics, such as a shrinking of the pseudo-lumen and a flow improvement in the true lumen, was well documented on serial MRI with Gd-DTPA and serial MRA.