Background: Clinical information about stroke in the vertebrobasilar territory has lagged behind that for anterior circulation syndrome. This is the first report from posterior circulation syndrome registry in Iran. Methods: Consecutive patients with brain infarction in vertebrobasilar territory admitted to Ghaem hospital, Mashhad were enrolled in a prospective study during 2006-2007. Diagnosis of ischemic stroke in the posterior circulation was made by a stroke neurologist based on the clinical manifestations and neuroimaging. Vertebrobasilar territory infarcts were classified into five groups according to the location involved: brainstem, thalamus, cerebellum, posterior cerebral artery, and mixed categories. All of the stroke patients underwent a standard battery of diagnostic investigations and the etiology of ischemic stroke was determined by the Practical Iranian Criteria classification. The 72-hour stroke course determined as regressive, stable, and deteriorative. Results: Total of 302 patients (147 females, 155 males) with mean age 62.5 years (±17.2) were investigated. Posterior cerebral artery, thalamus, brain stem, cerebellum, and mixed categories consisted 31.3%, 4.3%, 32.8%, 17.9%, and 13.9% of the stroke topographies respectively. Atherosclerosis consisted 50.6% of etiologies in our patients followed by uncertain (25.5%), cardioembolism (12.5%), both atherosclerosis and cardioembolism (6.3%), and miscellaneous causes (4.6%). Rheumatic mitral stenosis was the cause in 34.2% of our patients with cardiac emboly. The distribution of stroke etiologies based on its localization was not significantly different (df=16, and P=0.421). Stable status was the most common early stroke course (57.7%) followed by deteriorative (22.1%), and regressive (20.2%). A significant association between stroke localization in the vertebrobasilar territory and its course was not found (df=8, and P=0.901). Conclusion: Atherosclerosis is the most common cause of posterior circulation syndrome in Iranian patients. The cause of stroke in the posterior circulation could not reliably be derived from infarct topography.