A systematic review of the evidence was conducted on the benefits and adverse effects of hyperbaric oxygen treatment (HBOT) for cerebral palsy (CP). Studies of any HBOT regimen in patients with CP were included except for case reports and case series. Electronic databases (e.g. MEDLINE, EMBASE), professional society databases, and reference lists were searched to identify studies. Study quality was assessed using predefined criteria relevant to the study design. Two randomized controlled trials and four observational studies were identified. Best evidence came from a randomized controlled trial which found that HBOT at 1.75 atmospheres (atm) and 1.3atm of room air resulted in similar improvements in motor function (5–6%). Other outcomes also indicated no difference between the HBOT and room air. Observational studies reported improvements in motor function to a similar degree. Other evidence was insufficient to clarify the benefits and/or adverse effects of HBOT for CP. Both HBOT and pressurized room air resulted in improvements in motor function compared with baseline. Similar improvements were seen in the observational studies. Children undergoing HBOT were reported to experience adverse events, including seizures and the need for ear pressure equalization tube placement, but the incidence was unclear. Future research is needed to determine the efficacy of pressurized room air or non-pressurized oxygen in equivalent amounts by mask, compared with standard treatments.