Identification of stroke etiology aids in developing secondary prevention and treatment strategies for posterior circulation stroke (PCS). Studies have identified large vessel atherosclerotic disease as the predominant etiology and others have cited cardioembolism. This study was designed to describe the prevalence, outcome, and stroke mechanisms of PCS and to analyze the strengths and weaknesses of the classifications used.A comprehensive MEDLINE search identified seven studies evaluating the etiology of PCS. Incoherent data and lack of prospective studies made performance of a thorough meta-analysis impossible. Special attention was paid to the design of trials and the classifications used. In a similar way, the limitations of each study were clearly determined.Seven trials encompassing 8057 patients, of which 23% were isolated PCS and 4% were combined ACS and PCS, were analyzed. Overall, large vessel atherosclerotic disease was responsible for 35% of PCS, cardioembolism for 18%, small vessel disease for 13% and undetermined etiology for 15%. Strokes of mixed and "other" etiology represented 4% and 8% of PCS respectively. Major sequelae were observed in 10.8-17.7% of patients with no sequelae noted in 7-28% of patients. Mortality ranged from 4-10% and it was directly related to stroke in 2-5%.Large vessel atherosclerotic disease was the most common stroke subtype identified. Conclusions are inconsistent between the studies, highlighting the difficulties in systematic investigations of stroke etiology and the need for a unified approach to stroke classification.