Introduction: The emergency department is one of the most important departments of any hospital, where patients or their companions may not be satisfied with the services provided due to various reasons. This study aims to investigate the causes of the complaints of patients visiting the emergency department at Be’, sat Hospital in Hamedan, Iran in 2018-2019. Methods: In this cross-sectional study, all the complaints made over the years 2018 and 2019 from the emergency department of Ba’, ath Hospital in Hamedan, Iran were investigated. Demographic information, causes of complaint, sources of complaint, results of complaints and the complaint section were collected. Results: One hundred and seventy complaints were filed in two years. One hundred and nineteen cases (68. 4%) were filed by the patient’, s companions. Half of the patients who complained had university education. The postponement in the visit and assignment of the patient by the doctor, inappropriate treatment of the treatment staff, medical malpractice and wrong diagnosis were the most important reasons for the client complaints. In 45% of the cases, the patient or the patient’, s companion was right. Meanwhile, 39. 1% of patients had no convincing reason to complain and 15. 5% of their complaints were unsuccessful. A significant relationship was observed between the outcome of the complaint and education. Most of the registered complaints that were right with the patient were relevant to people with university education (P=0. 001). Conclusion: The findings of this study showed that postponement in the visit and assignment of the patient by the doctor, inappropriate treatment of the emergency personnel with the patient, medical malpractice, and wrong diagnosis are the most important causes of client complaints. Almost in half of the cases, the patient was right, which had a significant relationship with the level of education of the patients.