It is very important to make a prompt and accurate diagnosis and to commence pertinent treatment for patients suffering from acute cerebrovascular occlusive disease. Thirteen patients (mean age: 67.1 years) with basilar artery occlusion (BAO) were enrolled in this study. Dynamic computed tomography functional images (FID-CT) were analysed to determine whether this method could diagnose BAO in the acute phase. The functional images were categorized into 3 groups: (1) group A (n = 5) showed abnormalities on corrected mean transit time (cMTT) images and time-to-peak (TP) images in the territory of the posterior cerebral artery (PCA) and in the thalamus, (2) group B (n = 6) only showed abnormalities on TP images, and (3) group C (n = 2) had no abnormalities on either cMTT or TP images. The group C patients had poor time-density curves because of heart disease. Although the results may sometimes be false negative and this limitation should be kept in mind, FID-CT seem to be useful not only for defining patients who need angiography but also those who need thrombolytic therapy for acute BAO.