Background: Complaints are expressions of dissatisfaction that need to be addressed and are a very effective tool for improving the quality of care and treatment services. This study was conducted to investigate the complaints received in 2020 in the treatment supervision department of the Iran University of Medical Sciences. Methods: The present study is a retrospective descriptive study. All registered complaints, including written, oral and telephone, were reviewed by the complaints officer of the treatment supervision office in 2020. The data obtained from the review of complaints provided by clients of affiliated centres, including personal information of the complainant, the complainant was classified in an Excel file and analyzed by using descriptive statisticsSuch as number and percentage. Results: Of the total number of complaints received in 2020 with 2121, the cases included complaints about the provision of care and medical services 809cases, tariff 301 cases, health and infection control 222 cases, the activity of unauthorized persons 194 cases, visit services 125 cases, defects, respectively, Technical equipment 76 cases, lack of licenses 76 cases, admission and clearance services 69 cases, induced demand 66 cases, drugs 64 cases,  how to deal 63 cases, center closure and non-service 20 cases, forgery and misuse 18 cases, illegal advertising 10 cases, manpower shortage 8 cases. Conclusion: It seems that by identifying the effective factors in the occurrence of complaints and dissatisfaction and adopting solutions regarding Training in improving behavioural, communication and professional skills, periodic monitoring visits, reporting functional deficiencies to affiliated centres to correct and eliminate deficiencies, can be done to satisfy and prevent dissatisfaction so that the patient and with a pleasant memory of the process if necessary, refer others to the mentioned centre if necessary.