ABSTRACTCarbon monoxide (CO) can cause mass intoxication, but no standard triage algorithm specifically addresses CO poisoning. The roles of some recent diagnostic tools in triage as well as treatment with hyperbaric oxygen are controversial. We describe a mass casualty case of CO poisoning involving 77 patients, with a focus on the triage and treatment options decided on-site. The reasons for choosing these options are reviewed, and the pitfalls that occurred and the lessons learned from this major incident are described. We discuss the potential to improve the management of such an event and strategies to accomplish this, including simplifying triage and administering oxygen to all exposed persons for 6 h. (Disaster Med Public Health Preparedness. 2018; 12: 373-378).