This study aims to describe the epidemiology of unintentional non-fire related CO fatalities in the UK and to relate this information to sources of CO. Data from the CO-Gas Safety Society (COGSS) database was analysed and compared with data from the English House Condition Survey (EHCS). There were 462 deaths from the COGSS database, from 1 January 1996 to 31 December 2007 inclusive. The relative risk for death due to non-gas vs gas fuels was 10.52 (95% CI 7.71-14.34). The main weakness of the study is the likely underascertainment of CO deaths in the database. However, this study has identified specific risk factors for CO-related deaths in the UK; the use of non-gas fuels has not previously been highlighted as a significant cause of CO poisoning, and the relative risk (although not the absolute risk) of CO-related fatalities from these fuels is substantial.