The course and outcome in terms of cerebral morbidity and hospital mortality in 79 severely carbon monoxide poisoned patients admitted to the intensive care unit during a period of 15 years is presented. Treatment consisted of administration of pure oxygen. Ninety-four per cent of the patients were artificially hyperventilated, and the majority of the patients were also treated with moderate hypothermia, steroid hormones and diuretics. Hospital mortality was 30%, and 14% of the patients were discharged after long-term hospital treatment with signs of brain damage. Due to the unpredictable cerebral course after the acute incident long-term follow-up is recommended.