To determine whether flow through the subclavian artery might be affected during extracorporeal membrane oxygenation (ECMO), 40 neonates were examined with color Doppler ultrasound during and after ECMO. Retrograde flow in the right vertebral artery, noted in 12 of the 40 neonates (30%), was consistent with vertebral steal. Brachial systolic velocity was significantly less (P less than .01) on the right than on the left side in neonates both with and without vertebral steal. When the arterial cannula was removed after ECMO, vertebral artery flow became antegrade with symmetric velocity. Brachial velocities became symmetric in infants without vertebral steal, but mild asymmetry persisted in neonates who had had vertebral steal. Only one neonate had clinical signs of arm ischemia, which resolved promptly after removal of the cannula. No surviving neonates (n = 11) had neurologic findings related to the vertebrobasilar insufficiency over a 12-22-month period of observation. Vertebral steal appears to be common during ECMO and is resolved after removal of the cannula.