CO poisoning is the commonest cause of toxic death. Carbon monoxide is colourless, odourless, and tasteless, and is produced under various conditions. When people inhale CO, the gas diffuses rapidly to the body and replaces oxygen at the level of haemoglobin, myoglobin, and other oxygen carriers. Subsequently, CO causes oxygen deprivation of all body tissues. CO also induces oxidative stress and systemic inflammation. After CO poisoning a broad variety of symptoms may occur. Survivors of CO poisoning often present with persistent neurological sequels or develop delayed neurological symptoms. There is poor correlation between carboxyhaemoglobin levels and clinical symptoms. The presence of coma, underlying co-morbid conditions and need for mechanical ventilation are the main prognostic factors. Management includes prompt extraction from the toxic environment and breathing 100% oxygen, although the role and practicalities of hyperbaric oxygen therapy remain controversial.