Background: Hospital readmission places a high burden on both health care systems and patients. Most readmissions are thought to be related to the quality of the health care system. Objectives: The aim of this study was to examine the causes and rates of early readmission in emergency department in a Tehran hospital. Patients and Methods: A cross-sectional investigation was performed to study readmission of inpatients at a large academic hospital in Tehran, Iran. Patients admitted to hospital from July 1, 2014 to December 30, 2014 via the emergency department were enrolled. Descriptive statistics were used to summarize the distribution demographics in the sample. Data was analyzed by chi2 test using SPSS 20 software. Results: The main cause of readmission was complications related to surgical procedures (31.0%). Discharge from hospital based on patient request at the patient’s own risk was a risk factor for emergency readmission in 8.5%, a very small number were readmitted after complete treatment (0.6%). The only direct complication of treatment was infection (17%). Conclusions: Postoperative complications increase the probability of patients returning to hospital. Physicians, nurses, etc., should focus on these specific patient populations to minimize the risk of postoperative complications. Future studies should assess the relative connections of various types of patient information (e.g., social and psychosocial factors) to readmission risk prediction by comparing the performance of models with and without this information in a specific population.