BACKGROUND: We used transcranial Doppler to examine changes in cerebral blood flow velocity in children treated with extracorporeal membrane oxygenation. We examined the association between those changes and radiologic, electroencephalographic, and clinical evidence of neurologic injury. METHODS: This was a retrospective review and prospective observational study of patients 18 years old and younger at a single university children's hospital. Transcranial Doppler studies were obtained every other day during the first 7 days of extracorporeal membrane oxygenation, and 1 additional study following decannulation, in conjunction with serial neurologic examinations, brain imaging, and 6- to 12-month follow-up. RESULTS: The study included 27 patients, the majority (26) receiving veno-arterial extracorporeal membrane oxygenation. Transcranial Doppler velocities during extracorporeal membrane oxygenation were significantly lower than published values for age-matched healthy and critically ill children across different cerebral arteries. Neonates younger than 10 days had higher velocities than expected. Blood flow velocity increased after extracorporeal membrane oxygenation decannulation and was comparable with age-matched critically ill children. There was no significant association between velocity measurements of individual arteries and acute neurologic injury as defined by either abnormal neurologic examination, seizures during admission, or poor pediatric cerebral performance category. However, case analysis identified several patients with regional and global increases in velocities that corresponded to neurologic injury including stroke and seizures. CONCLUSIONS: Cerebral blood flow velocities during extracorporeal membrane oxygenation deviate from age-specific normal values in all major cerebral vessels and across different age groups. Global or regional elevations and asymmetries in flow velocity may suggest impending neurologic injury.