Background/Aims: It is crucial to detect the composition of the thrombus in isolated brainstem infarction with large artery occlusion. The aim of this study was to explore the susceptibility vessel sign (SVS) whose composition is mainly deoxidized red cells in patients with isolated brainstem infarction and posterior circulation large artery occlusion. Methods: This was a single-center retrospective study. All patients with posterior circulation large artery occlusion from January 2003 to September 2013 were included. We identified 213 patients who had posterior circulation large artery occlusion, and 81 patients met the imaging eligibility criteria. Among the 81 patients, 21 had isolated brainstem infarction. Results: Among the 21 patients, 7 (33%) had SVS and 2 (10%) had pseudo-SVS (calcified vessels without thrombosis). In the 7 patients with SVS, we found atrial fibrillation in 2 patients, dissection in 3 patients and large artery atherosclerotic disease (LAAD) in 2 patients. There were SVS in 100% (2/2) of patients with atrial fibrillation, 50% (3/6) of patients with dissection, and 20% (2/10) of patients with LAAD. Conclusions: SVS reflects pathology of deoxidized red cells composition in patients with isolated brainstem infarction. This finding may be useful to explore the different stroke mechanisms and therapy strategies.