PURPOSE: To evaluate the characteristic color Doppler imaging of vertebral artery flow in the subclavian steal phenomenon. MATERIALS AND METHODS: The study group consisted of eight patients with reversed vertebral artery flow proved by color Doppler imaging. We classified this flow into two groups : (1) complete reversal ; (2)partial reversal, as shown by Doppler velocity waveform. Vertebral angiography was performed in six of eight patients ; color Doppler imaging and angiographic findings were compared. RESULTS: On color Doppler imaging, all eight cases with reversed vertebral artery flow showed no signal at the proximal subclavian or brachiocephalic artery. We confirmed shunting of six cases by performing angiography from the contralateral verterbral and basilar artery to the ipsilateral vertebral artery. On the Doppler spectrum, six cases showed complete reversal and two partial reversal. On angiography, one partial reversal case showed complete occlusion of the subclavian artery with abundant collateral circulation of muscular branches of the vertebral artery. CONCLUSION: On color Doppler imaging, a reversed vertebral artery suggests the subclavian steal phenomenon. In particular, partial reversal waveform may reflect collateral circulation.