Objective: We aimed to investigate the epidemiological characteristics and trends of carbon monoxide (CO) poisoning in the National Emergency Department Information System (NEDIS). Methods: Using the NEDIS data from 2014 to 2018, we included patients who had visited the emergency department (ED) with CO poisoning (T58.0 in 7th Korean Standard Classification of Diseases [KCD-7]). We excluded patients with an uncertain time of onset, uncertain intentionality of poisoning, mental state, and unknown clinical outcome. We surveyed age, sex, time of onset, the intentionality of poisoning, mental state, results of emergency treatment, the proportion of admissions to intensive care units (ICU), the outcome of hospitalization, and the regional distribution. We analyzed the rate of incidence and trends of CO poisoning in patients using time series analysis. Results: A total of 18,533 patients, including 10,671 (57.6%) males and 7,862 (42.4%) females, with a mean age of 40.38±18.41 years, were included in this study. Gyeonggi Province (n=6,354, 34.3%) had the highest distribution of patients, followed by Seoul (n=3,357, 18.1%). The incidence of unintentional CO poisoning was more frequent in January and December, and less frequent in August and September. However, the incidence of intentional CO poisoning showed no seasonal variation. The severity, ICU hospitalization rate, and mortality rate for intentional CO poisoning were higher than unintentional CO poisoning (4.1% vs. 0.8%, 29.9% vs. 16.7%, and 2.0% vs. 0.8% respectively) (P<0.001). Applying Winter’s additive method, we could predict that the rate of unintentional CO poisoning would continue to increase and the seasonal fluctuation, such as cases increasing in January-December and decreasing in August-September, would also increase. Conclusion Intentional CO poisoning showed higher severity than unintentional CO poisoning. In the time series analysis, the rate of unintentional CO poisoning and seasonal fluctuation is predicted to increase.