A patient undergoing coil occlusion of a left internal carotid artery aneurysm was investigated by continuous arterial spin labeling MR imaging to evaluate perfusion territory mapping. Labeling was restricted to the left- or right-sided carotid artery by use of a separate neck coil. Before embolization, perfusion contrast was largely restricted to the labeled hemisphere. After embolization, perfusion contrast was created symmetrically in both hemispheres on labeling the right side, verifying sufficient collateral supply.