AbstractObjectiveTo examine trends in the incidence of carbon monoxide poisoning before and after a ban on domestic use of raw coal in Ulaanbaatar, Mongolia.MethodsUsing injury surveillance data and population estimates, we calculated the incidence per 100 000 person-years of fatal and non-fatal domestic carbon monoxide poisoning before (May 2017 to April 2019) and after (May 2019 to April 2022) the ban in May 2019. We analysed data by age and sex, and compared areas not subjected to the ban with districts where domestic use of raw coal was banned and replaced with refined coal briquettes.FindingsWe obtained complete data on 2247 people with carbon monoxide poisoning during the study period in a population of around 3 million people. In districts with the ban, there were 33 fatal and 151 non-fatal carbon monoxide poisonings before the ban, and 91 fatal and 1633 non-fatal carbon monoxide poisonings after the ban. The annual incidence of poisoning increased in districts with the ban, from 7.2 and 6.4 per 100 000 person-years in the two 12-month periods before the ban to 38.9, 42.0 and 40.1 per 100 000 in the three 12-month periods after the ban. The incidence of poisoning remained high after the ban, despite efforts to educate the public about the correct use of briquettes and the importance of ventilation. The incidence of carbon monoxide poisoning also increased slightly in areas without the ban.ConclusionEfforts are needed to investigate heating practices among households using briquettes, and to determine factors causing high carbon monoxide concentrations at home.