Carbon monoxide is a colourless, odourless and tasteless gas existing in a miniscule concentration in the atmosphere (< 0.001%), and is a product of partial combustion. Carbon monoxide poisoning is associated with a high incidence of morbidity and mortality. Symptoms are usually non-specific and include fatigue, headache, dizziness, nausea and vomiting, cognitive impairment, and tachycardia; mimicking an influenza-like illness. Symptoms occurring in more than one person (belonging to the same family/office) simultaneously and the relief also occurring at the same point of time in them should sound the physician’s mind for suspected carbon monoxide poisoning. A high index of suspicion and presence of a source of generation of carbon monoxide are the diagnostic aids which can be confirmed by blood carboxyhaemoglobin levels. Removal from the source of carbon monoxide generation, moving the person to fresh air immediately is most important. In the emergency room, oxygen therapy is the key. Immediate treatment with a high fraction of inspired oxygen and careful clinical evaluation are mandatory for effective management. Patients with a carboxyhaemoglobin level of 10% or more should always be treated and 100% oxygen for 8 hours is recommended for patients requiring artificial ventilation. Hyperbaric oxygen also holds promise in select cases specially those with a history of unconsciousness, cardiovascular instability or ischemia, persistent mental and/or neurologic deficits and probably in pregnant patients.