Carbon monoxide (CO) poisoning is an important clinical problem. The symptoms of poisoning are non-specific, particularly in the paediatric population. Currently, the use of hyperbaric oxygen (HBO) is considered to be more justified with increasing severity of the patient’s clinical status and with shorter time elapsed from CO exposure. Aim of the study: The aim of this study was to assess the efficacy of hyperbaric oxygen therapy in children with symptoms of carbon monoxide poisoning. Material and methods: The study was a retrospective analysis of medical records of children hospitalised for carbon monoxide poisoning at the Department of Paediatrics, Paediatric Nephrology and Allergology of the Military Institute of Medicine, Poland, between January and December 2018. The following data were analysed: laboratory test results, CO poisoning circumstances, the manner of reporting to the Department, the number of hyperbaric chamber sessions needed to relieve the symptoms completely, the occurrence of complications and the duration of stay at the Department after treatment completion. Results: The analysis of the results did not demonstrate any relationship between carboxyhaemoglobin level and poisoning manifestations and CO poisoning severity. However, a statistically significant positive correlation was demonstrated between carboxyhaemoglobin level and HCO₃− level and a statistically significant negative correlation was found between carboxyhaemoglobin level and capillary pH. No statistically significant differences were found between children with mild poisoning and those with severe poisoning in terms of potassium level, capillary pH, and HCO₃− and glucose levels. At the same time, it was demonstrated that hyperbaric therapy is a highly effective and safe method. Conclusion: Regardless of the causes of CO poisoning in the paediatric population, hyperbaric therapy is a highly effective and safe method. One session in a hyperbaric chamber is sufficient to relieve the symptoms completely and prevent delayed sequelae of poisoning and CO side effects.