Background & Aim: Determining the Minimum Data Set (MDS) is necessary to improve the quality of health care services and is the first important step in development of the hospital information system (HIS). The discharge information system is one of the essential sub-structures of a hospital, and its performance is critical regarding hospital costs and deductions. This research aimed to determine the minimum data set necessary for the discharge information system. Materials & Methods: This was a descriptive-applied study. The data collection tool was the questionnaire of the minimum data set of the discharge information system. In each determined case, the set of minimum data of the discharge information system was determined by users based on the fivepoint Likert scale and using the opinions of 11 experts in two stages of the Delphi technique. SPSS v. 21 and Atlas TI softwares were used for data analysis. Results: The minimum data set of this system was 128 data elements in seven main categories, including patient identification and personal information, clinical, administrative-financial and identity user access levels, patient insurance information, health service providers, financial data, Patient billing, patient discharge data, billing and patient discharge from the center, which were determined and approved by experts. Conclusion: Discharge information systems with MDS at the national level can play an important role in reducing costs, evaluating treatments, and improving quality, and can be considered a standard tool for collecting and recording hospital information.