Introduction: Poisoning is one of the causes of consciousness loss that should always be considered. Carbon monoxide is a no-smelling, color and taste that is highly toxic. If we do not think of this poisoning, the diagnosis is difficult and may be mistaken with other poisoning. Case presentation: Emergency reported when arrived to patient’, s home, found 3 patients in different areas. The family's mother, along with the stove, while cyanotic and having pulse and also found 3 canned fish near her The father was found next to the toil while he was confused. The 15-yearold daughter was found along with her moth without clinical vital signs. The autopsy of girl reported that the cause of death was poisoning with carbon monoxide with carboxy-hemoglobin level 50. Accidental poisoning with carbon monoxide has been reported in several articles. The variable symptoms lead to misdiagnosis in 1/3 cases. The definite diagnosis is made by carboxy-hemoglobin measurement, in non-smoker patients, carboxy-hemoglobin level of 2-3% and greater than 9% in smoker patients. Conclusion: Carbon monoxide poisoning is a lethal condition,this poisoning may be miss-diagnosed or not diagnosed. At the beginning of the cold season, we should consider this diagnosis.