Objective To evaluate the value of the clinical use of CT perfusion imaging (CTPI) and CT subtraction angiography (CTSA) for diagnosing acute ischemic cerebrovascular disease (AICVD). Methods Twenty-four patients with AICVD onset within 24 hours were examined with regular CT, CTPI, and CTSA. Some cases received CTPI, magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), digital subtraction angiography (DSA) or single photon emission computer tomography (SPECT) during follow-up examinations.Results Of the 24 cases, 11 had negative results from regular CT scans 3-6 hours after onset of stroke in 6 cases, 6-12 hours in 3 cases, and 12-24 hours in 2 cases. Ten of these cases were then confirmed by CTPI as having ischemic lesions, 2 with middle cerebral artery occlusion (MCAO), and 1 case with transient ischemic attack (TIA) with CTPI negative. Of the 24 cases, 13 had positive results from regular CT, 9 were diagnosed with ischemic lesions larger by using CTPI than regular CT, 1 case had MCAO and 1 had internal carotid artery occlusion (ICAO). There were 4 cases with ischemic lesions observed with regular CT having nearly the same range as that of lacunar infarctions using CTPI. Another 4 cases had more than 2 lesion areas. The peak time (PT), mean transit time (MTT) and relative flow (RF) of 24 cases were markedly different. The sides of ischemic lesions compared to each other and the core of the lesion compared to peripheral zones were also altered significantly (P<0.01).Conclusions Combined CTPI with CTSA can detect acute ischemic lesions at early and hyper-early stages and could distinguish between TIA, lacunar infarction and a larger area of infarction. Using semiquantitative blood perfusion analysis status, CTPI with CTSA could define position, area and range of the ischemic lesion and penumbra. These scans can also analyze the brain blood perfusion status. It is important to early diagnose the occlusion of the entire division of the internal carotid artery or middle cerebral artery and it is meaningful to assess prognosis and assignment of therapy.