Treatment protocol of renal transplantation changed from Azathioprine to Mycophenolate mofetil (MMF) in Iran, at 2000. However this change could have a great impact on post kidney transplantation outcomes, but it has not been studied fully, yet. We designed this study to investigate the impact of this change on the causes of re-hospitalization. In Baqyiatallah hospital, Tehran, Iran; 524 post transplantation admission records were randomly selected, 202 of them had been admitted before the year 2000 (Group I) and 322 after that time (Group II). The causes of admission were categorized into renal dysfunction, infection, surgical complication, and macrovascular disease. Proportion of each cause compared between the two groups. Admissions related to renal dysfunction decreased from 53% to 31%, after the year 2000 (p=0.02). Instead, 33% of admissions in Group I and 47% in Group II were due to infections (p=0.01). Admissions due to macrovascular diseases, cancer and surgical complications were the same in two groups. The mean age at admission, time interval between transplantation and admission and the length of hospitalization were not significantly different (p>0.05). A marginally significant increase in mortality rate of inpatients (3% vs. 7%, 0.05 Changing of a transplantation treatment protocol is a complex process. While changing the treatment protocol from Azathioprine to Mycophenolate mofetil has its own advantages, other complications, such as high infection rate, have emerged. It is important to modify the follow-up and caring modalities according to the new situation.