Emergency Department (ED) is considered as one of the most important clinical departments in a hospital and the 1st line between the patients and the entire hospital departments. In fact, this department is usually overcrowded, which might lead to a crisis such as leaving the patients in ED before checking or seeing doctors. Patients who leave emergency departments (EDs) without being seen are common in many hospitals. These patients may represent a safety concern. Those patients who leave without being seen (LWBS) for avoiding staying a long time and other reasons have been shown to have deterioration of their medical condition necessitating admission, urgent surge and various medical errors occur, which may have a connection with several factors that are related to staff and clarity of information. These factors participate to give a perfect outcome including patients' satisfaction result in reducing the incidence of patients leaving without being seen. (LWBS). Using the Canadian Triage and Acuity Scale (CTAS) in the majority of ED in public hospitals of Saudi Arabia, the number of patients LWBS is considered as one of the keep performance indicators (KPI) of the emergency departments. This study provides a list of possible factors that result in increasing this number and the solutions for limiting these serious complications are very important. Also, it could show several reasons that can affect the KPI of the ED. Moreover, a literature review has been performed to identify the factors that affect patients leaving without been seen. Few studies have been conducted in Saudi Arabia related to factors affecting patient LWBS by a physician. However, none of them was in KSMC