Re-admission following kidney transplantation is an extremely costly aspect of health care. We sought to investigate what factors were the principal causes of re-admission in different postkidney transplantation periods. In this retrospective analysis, 562 randomly selected re-admissions of kidney recipients in Baqyiatallah Hospital from 1994 to 2006 were divided into 3 groups: Group 1: within the first 6 months (n=278); Group 2: between 6 – 24 months (n=115); and Group 3: 24 months and afterwards (n=169). The groups were compared in terms of demographic variables, lengths of hospital stay, causes of endstage renal disease (ESRD), and fatalities. Infections (p=0.01) and surgical complications (p=0.03) were significantly more common, but malignancies was less common (p=0.05) in Group 1 in comparison with the other two groups. The length of hospital stay was also significantly longer in Group 1 (p=0.001). Mortality remained the same in the three groups (p>0.05). Age at admission, sex, and cause of ESRD were not significantly different between the three groups (p>0.05). In early post-kidney transplantation phase, infections and surgical complications put the kidney transplant recipients at a higher risk of re-hospitalization than do malignancies. These findings can be used to better design time-specific preventive programs. The self-care education should be more focused on infections and surgical complications in earlier stages and malignancies later on.