The aim of this study was to review the imaging features in acute (< 24 h) basilar artery thrombosis. CT and MR studies in 11 patients with clinical diagnosis of acute basilar artery thrombosis were retrospectively reviewed. MR angiography was obtained in 4 patients. Correlation with clinical symptoms was performed. Multiple cranial nerve palsies and hemiparesis were the most common clinical symptoms at presentation. CT revealed hyperdense basilar arteries (n = 7) and hypodensities in the posterior circulation territory (n = 8). In one instance, the infarction was hemorrhagic. MR imaging showed absence of flow void within the basilar in 6 patients and MRA (using both PC and TOF techniques) confirmed absence of blood flow in 4 basilar arteries. One week after presentation, 5 patients died. Autopsy was obtained in 1 case and confirmed the diagnosis of basilar artery thrombosis. Basilar artery thrombosis has fairly typical imaging features by both CT and MR. MRA may be used to confirm the diagnosis. Prompt recognition may lead to early thrombolytic treatment and may improve survival.