The primary aim of this study are to gather data on the "real world" experience of the Penumbra System and to determine if there is a correlate between the imaging-defined size of the ischemic penumbra at admission and patient outcome in patients already treated by the System. This will be accomplished by the collection of all available admission imaging data along with patient clinical and functional outcome results at 90-day follow-up to determine if a positive association exists between these variables. A secondary aim is to collect and summarize the 90-day functional outcome data for the purpose of sample size estimation for a potential randomized concurrent controlled trial. This will be accomplished by collecting the data on 90-day modified Rankin Scores (mRS) and all cause mortality.