Materials and Method:  This is a descriptive and cross- sectional study consisting of 9 hospitals. The samples were consisted of patients who readmitted in hospitals affiliated to Tehran University of Medical Sciences. The required information has been registered in a questionnaire by means of computer, admission forms and index cards. The medical records of 250 patients were collected and analyzed by t test, Fisher Exact Test and Chi Square test.

Result: 17.8% of understudy patients were admitted two times and 80.7% were admitted more than two times in the hospital. Most of these 80.7% of patients were over 60 years old. It was seen a significant relation between patients' age and readmission also occurring infection. In categorizing diseases according to the reason of patients' readmission (23.1% in the second period and 20.2% in the third period) encountered diseases related to body blood system while readmitting in the hospital. The average cost of patients bedridden admitted for the second and third times because of the same reason was 3241532 and 1576593 tomans. There was a significant relationship between readmission and length of stay in both periods. Pursuit of treatment in 101 cases with average cost of 1802757 tomans in second time and 84 cases with average cost of 1205283 tomans in the third period was among the highest costs of readmission causes. Also the highest length of stay was related to surgery unit (9.98 days). The highest average of patients' costs related to surgery unit was 3543854 and 3911168 tomans for second and third periods.

Conclusion: Most of readmissions are among 60 years old patients and the most important reasons for the second and third readmissions are as a result of treatment follow up, adverse effect and illness complication which can be for the reason of incomplete treatment, non compliance of clinical protocols and lacking standard instruments. Results show that readmissions can increase patients' length of stay and additional burden of costs for patients, hospitals and insurance institutes. Therefore we can prevent these unnecessary costs and increase patients' satisfaction by complying clinical protocols, standardizing hospital procedures and instruments, personnel training and using new methods of diagnosis and treatment. The reform in Health care policies and focusing on the health care quality on the side of the administrators also paying more attention to home visits and home care are recommended to this case.