Subclavian steal syndrome may result from stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery. The diagnosis can be confirmed by noninvasive vascular studies with the use of a directional Doppler probe or by time-sequence aortic arch angiography, both of which can detect retrograde flow in the vertebral artery. A variety of surgical approaches to this condition have been used in the past, but the simpler and much safer carotid-to-subclavian bypass has become a more acceptable surgical procedure. There remains, however, a theoretical possibility that blood may be siphoned from the intracranial arteries perfused by the carotid. This phenomenon, which may be called the carotid steal syndrome, has been discussed, but no clinical cases have been reported. We present a patient who developed such a carotid steal syndrome 2 years after left carotid-subclavian bypass. This occurrence reemphasizes the importance of determining a normal carotid bifurcation prior to performing carotid-subclavian bypass.