Carotid or cerebral artery stenosis resulting in low perfusion is a major cause of ischemic stroke. Understanding the unique hemodynamic features in each patient undergoing a stroke-in-progress (SIP) and the correlation between progression and cerebral blood flow (CBF) status would help in the diagnosis and treatment of individual patients. We used xenon-enhanced CT (Xe-CT) to examine cerebral perfusion in patients with or without SIP (30 patients/group), recruited from October 2009 to October 2010. Only SIP patients with unilateral stenosis in the internal or middle cerebral artery were recruited. The occurrence of watershed infarction was higher in the SIP group than in the non-SIP group (P <0.05). In the SIP group, larger hypoperfused areas were found around the lesions than in the non-SIP group. In the SIP group, the CBF values in the ipsilateral areas were significantly lower than those in corresponding regions on the contralateral side. CBF values in the contralateral hemisphere were significantly lower in the SIP group than in the non-SIP group. In SIP patients, infarctions were surrounded by larger hypoperfused areas than in non-SIP patients. These larger hypoperfused areas may result in pathological damage to the brain that is responsible for the progression of stroke.