Abstract: Objective: To investigate the MRI features and etiology of acute cerebral infarction in bilateral PICA territory. Methods: 38 patients with bilateral PICA and 40 patients with bilateral SCA diagnosed clinically and radiographically in Beijing Friendship Hospital of Capital Medical University from January 2019 to January 2022, were retrospectively analyzed. The difference of MRI features, were compared between the two groups, according to the size of the infarction, the distribution of infarcted lesions in posterior circulation or anterior circulation. The range of acute infarction in the bilateral PICA territory and the changes of vertebrobasilar artery were analyzed. Results: The proportion of the infarction model of one side regional infarction with the other side small infarct in bilateral PICA was significantly higher than that in bilateral SCA (39.5% vs. 15%), while the model of small infarction on both sides was lower than that in bilateral SCA (44.7% vs. 72.5%). The incidence of infarction in other blood supply areas of the combined posterior circulation was significantly lower than that in bilateral SCA (21% vs. 80%). The infarction models of bilateral PICA manifested as unilateral total infarct of PICA territory combined with the other unilateral infarct of mPICA territory (44.7%) or bilateral mPICA territory (39.5%). Unilateral vertebral artery V4 segment or PICA-localized severe stenosis/occlusion were more frequently detected in acute infarcts in bilateral PICA (54.2%). Conclusions: Bilateral PICA territory infarction mainly manifested as unilateral total infarct of PICA territory combined with the other unilateral or bilateral infarct of mPICA territory, and regional infarction was quite common, which was closely related to anatomical variation.