Accurate classification of stroke is important. The Trial of ORG 10172 in Acute Stroke Treatment (TOAST) classfication has been widely used to determine etiology of ischemic stroke. The iClass is application for helping stroke classification, iClass has a computerized algorithm, which can reduce burden of recalling classification criteria by interactive response to select each steps. Displaying flowcharts can ensure exact calssification. Ancillary information including definition of potential cardiac sources of embolism, classic lacunar syndrome, and rare causes of stroke are provided.