Aim: To observe the cerebral infarction patterns and distribution of atherosclerotic middle cerebral artery stenosis, and investigate the pathophysiological mechanism of cerebral infarction induced by atherosclerotic middle cerebral artery stenosis. Methods: The MRI data of 50 patients, who were diagnosed to have symptomatic middle cerebral artery stenosis by cerebral angiography in Beijing Tiantan Hospital between June 2004 and August 2005, were retrospectively analyzed, the stenosis rate was > 50% in all the patients, and they were not accompanied by ipsilateral internal carotid artery stenosis or occlusion, they all had at least 1 atherosclerotic risk factor, and their infarction patterns were categorized and observed. Results: The neural imaging data of the 50 patients with middle cerebral artery stenosis showed that subcortical infarction was the most common, including 44% were deep perforator infarction and 42% were internal border-zone infarction; 6% and 2% were cortical and territorial infarction respectively; 14% were cortical spotty lesion, 12% and 24% were anterior and posterior border-zone infarction respectively. Conclusion: Various cerebral infarction patterns may occur in atherosclerotic middle cerebral artery stenosis, it is suggested that middle cerebral artery stenosis can lead to different pathophysiological mechanism of cerebral infarction.