Objective: A suicide attempt by self-poisoning is a common cause of admissions to the emergency department (ED). Management of such intentiona poisoning often requires complicated medical procedures, resulting in a longer length of stay (LOS) as compared to other cases that require treatment in the ED. This study aimed to determine the factors affecting a longer LOS in self-poisoning patients. Methods: This was a retrospective study wherein all the medical charts of patients who visited the ED of one hospital, from August 2016 to July 2019, because of intentional self-poisoning, were reviewed. Results: Most of the patients visited the ED involuntarily and there were almost twice as many female patients as males. Almost half of the patients were referred to the psychiatry department. A comparison of various factors within the LOS groups revealed significant differences in mental status, guardian co-visitation, patient gender, psychiatric referral, and poisoning substance. Moreover, the LOS had a stronger association with the pre-consultation period than the consultation to decision-making period. Conclusion To reduce the LOS, it seems important to make a rapid decision on whether to observe the patient in the ED and wait until the workup is completed or to admit and then evaluate the patient in the ward. If the clinicians cannot obtain enough information to evaluate the patient for appropriate management, short-term admission may be an option to reduce the LOS and to provide a stable evaluation.