Purpose: The purpose of this study was to identify the changes in the characteristics of patients with carbon monoxide (CO) poisoning, as well as the distinctive differences in intentionally exposed patients. Methods: The medical records of CO poisoning patients, who visited nine emergency departments between January 2010 and December 2011, were reviewed retrospectively. The clinical information including age, gender, hospitalization, type of discharge, cause and location of exposure, site of onset, concentration of initial blood carboxyhemoglobin (COHb), methods of treatment and presence of neurological complications was examined. The subjects were divided into an intentional and non-intentional group and the differences between them was compared. Results: A total 209 subjects were recruited. The median age was 38 years (29~49.5 years). They frequently complained of nausea and vomiting, and the most common exposures occurred in winter, normally in the home. The cause of exposure was usually fire, followed by incomplete combustion of fuels. The median initial blood COHb was 13.15%. The proportion of intentionally exposed patients was 21%. They were significantly younger, more frequently discharged against medical advice, and showed a higher initial blood COHb level (22.85%) than the non-intentional group. Conclusion: This study suggests that those with intentional CO poisoning are normally discharged against medical advice even when they have a higher initial COHb level. An adequate explanation of the delayed neurologic sequelae and short term follow-up observation is recommended for those patients with intentional exposure.