Carbon monoxide poisoning is one of the most common lethal poisonings. Neurological or psychiatric sequelae occur in approximately 50-75% of survivors. Carbon monoxide poisoning can be treated with 100% oxygen or hyperbaric oxygen. The Glasgow Coma Scale (GKS) of the male patient who was admitted to our emergency department with CO intoxication due to a heater was 4. The patient’s transport to a hyperbaric oxygen treatment center was considered but the conditions were not suitable for transport, so 100% oxygen treatment with mechanical ventilator was initiated. The patient was weaned from the mechanical ventilator at day 5 and he was extubated when his spontaneous breathing was adequate. He was discharged from hospital at the end of the follow-up period, day 14. His general condition was quite good and his GKS was 15 at discharge . Although most of the studies suggested that hyperbaric oxygen treatment was more efficacious in carbon monoxide poisoning, other studies stated that there was no difference between hyperbaric oxygen and 100% oxygen treatment.There is a general opinion that the supportive treatment is very important for survival.