ObjectivesThe aim was to describe population-based incidence and emergency department-based prevalence and 1-year all-cause mortality of patients with new organ failure present at arrival.DesignThis was a population-based cohort study of all citizens in four municipalities (population of 230 000 adults).SettingEmergency department at Odense University Hospital, Denmark.ParticipantsWe included all adult patients who arrived from 1 April 2012 to 31 March 2015.Primary and secondary outcome measuresOrgan failure was defined as a modified Sequential Organ Failure Assessment score≥2 within six possible organ systems: cerebral, circulatory, renal, respiratory, hepatic and coagulation.The primary outcome was prevalence of organ failure, and secondary outcomes were 0–7 days, 8–30 days and 31–365 days all-cause mortality.ResultsWe identified in total 175 278 contacts, of which 70 399 contacts were further evaluated for organ failure. Fifty-two per cent of these were women, median age 62 (IQR 42–77) years. The incidence of new organ failure was 1342/100 000 person-years, corresponding to 5.2% of all emergency department contacts.The 0–7-day, 8–30-day and 31–365-day mortality was 11.0% (95% CI: 10.2% to 11.8%), 5.6% (95% CI: 5.1% to 6.2%) and 13.2% (95% CI: 12.3% to 14.1%), respectively, if the patient had one or more new organ failures at first contact in the observation period, compared with 1.4% (95% CI: 1.3% to 1.6%), 1.2% (95% CI: 1.1% to 1.3%) and 5.2% (95% CI: 5.0% to 5.4%) for patients without. Seven-day mortality ranged from hepatic failure, 6.5% (95% CI: 4.9% to 8.6%), to cerebral failure, 33.8% (95% CI: 31.0% to 36.8%), the 8–30-day mortality ranged from cerebral failure, 3.9% (95% CI: 2.8% to 5.3%), to hepatic failure, 8.6% (95% CI: 6.6% to 10.8%) and 31–365-day mortality ranged from cerebral failure, 9.3% (95% CI: 7.6% to 11.2%), to renal failure, 18.2% (95% CI: 15.5% to 21.1%).ConclusionsThe study revealed an incidence of new organ failure at 1342/100 000 person-years and a prevalence of 5.2% of all emergency department contacts. One-year all-cause mortality was 29.8% among organ failure patients.