BACKGROUND Carbon monoxide (CO) poisoning results in hundreds of deaths and thousands of emergency department visits all over Iran annually. In this study, we aim to provide an epidemiologic analysis of this poisoning in different consciousness levels. METHODS This single-center retrospective study was conducted at a referral poison center from March 21, 2007 to March 19, 2012 in Tehran, Iran. All CO poisoned children and adults who hospitalized were evaluated based on their on-arrival consciousness level. RESULTS Two-hundred-sixty patients with pure CO poisoning were enrolled with the majority of males (55.4%). CO exposure was unintentional in 99.6% of cases. The average period between CO exposure and the patients' hospital admission was 6.4 hours (SD = 11.2). Most of the toxicities had occurred at home (73.5%). On arrival acid-base status revealed respiratory acidosis cases in 11.9% of cases. Central nervous system imaging revealed 6.2% abnormal finding. Typically, patients presented with vomiting (25.8%), nausea (22.7%), and dizziness (11.3%). Twenty-nine patients (11.2%) needed intubation and mechanical ventilation. Thirty-six patients admitted to ICU with a median [IQR] hospital stay of 6 [2, 18] days. Ultimately, 202 (78.6%) patients discharged and 47 (18.3%) left the hospital against medical advice, 5 (1.9%) died, and 10 (3.8%) experienced sequellae. Two patients (0.8%), were transferred to other hospitals for specialized care. CONCLUSIONS The incidence and mortality rate of CO poisoning in the current study are still higher than many other parts of the world. Ongoing health prevention strategies are not efficiently working. Hence, constant public education and warning about CO toxicity should be highlighted.