Treatment of brain embolism should depend on the nature of the embolic material, if discoverable or predictable, not on whether the source was cardiac or intra-arterial. The middle cerebral artery territory is the most common recipient site for emboli, but many emboli do go to the carotid arteries and the posterior circulation. Cardiac and intra-arterial embolism probably each account for about one in five posterior circulation infarcts. Paradoxical embolism is much more common than formerly appreciated. The carotid arteries are probably the most common sources of intra-arterial emboli to the brain, but emboli also frequently arise from the aorta and the vertebral arteries. Potential embolic materials probably frequently enter the circulation but rarely cause strokes.