Taiwan is an island situated in the subtropics. The lowest average temperature is around 15 degrees C (59 degrees F) during winter). Despite the mild climate, carbon monoxide intoxication still occurs frequently, especially during the winter. We studied which meteorological factor(s) affected the occurrence of carbon monoxide poisoning in Taiwan. Retrospective data over a period from December 1, 1986, to December 31, 1991, from patients who reported with carbon monoxide poisoning to the Poison Control Center, together with meteorological data were analysed. We found that a lower daily average temperature, especially while a special regional circulation pattern, called a 'cold front' or 'cold surge' (during winter) covers the Taiwan area, is strongly related to the occurrence of CO poisoning.