Introduction : Carbon monoxide (CO) is a colourless, odourless, tasteless toxic gas produced by incomplete combustion in fuel-burning devices such as motor vehicles, gas-powered furnaces, and portable generators. Exposure of humans to high concentrations of carbon monoxide can result in death, due to the formation of carboxyhemoglobine (COHb), which impairs the oxygen carrying capacity of the hemoglobin. The objective of this study was to determine the number of carbon monoxide-related deaths in forensic cases received in the Department of Seville of the Spanish National Institute of Toxicology from 2000 to 2006 ( n=515 cases). Methods : Carboxyhemoglobine levels were determined in blood using the normal procedure in our laboratory, consisting in a fourth derivative spectrophotometric method, using sodium dithionite as releasing agent. COHb levels were then measured after the saturation of blood with carbon monoxide. Results : In 415 of these cases (81%) carboxyhemoglobine was detected. In a 33% of the cases COHb was above 50% and in a 48% of the cases was below 50%. During the period studied males represented the big majority 72% of deceased people, presenting a 35% of the cases levels of COHb above a 50%. In a 26% of the cases the deceased was female with a 34% of the cases, which resulted in a COHb level above 50%, and in a 2% of the cases sex was not known. Conclusions: Our results indicate that improved population-based prevention measures, including educating the public about the dangers of CO exposure, are needed in order to avoid domestic accidental deaths.