Cyclosporine (Cs-A) is a cornerstone of the immuno­suppressive treatments after kidney transplantation. However, it carries significant nephrotoxicity. Cs-A withdrawal and use of sirolimus (SRL) is associated with improvement of renal function. In this study, safety and efficacy of SRL conversion in kidney transplant recipients was sought. In 63 kidney transplant recipients, Cs-A was discontinued and SRL started. A preconversion kidney biopsy was performed in 52 patients. The major cause for biopsy was increased serum creatinine in 48 patients. Serum creatinine and GFR were measured at conversion and at 1, 3, 6 and 12 months post conversion. The occurrence of adverse effects of SRL was also evaluated. The major cause for conversion according to the preconversion kidney biopsy was Cs-A nephrotoxicity in 33 patients followed by chronic allograft nephropathy (CAN) in 13. Mean time to conversion was 60.9± 5 months. The number of post conversion biopsies was low and we could not evaluate the impact of conversion on pathologic changes in the kidney. The mean follow up time was 10± 8.3 months. The mean GFR at time of conversion was 56.78± 17.89 cc/min. It improved significantly during follow up. The mean GFR was 62.31± 15.8, 59.75± 15.87, 59.51± 17 and 58.62± 20.79 at 1, 3, 6 and 12 months, respectively. Common adverse effects of SRL included anemia in 9, thrombocytopenia in 2, anemia and thrombocytopenia in 1, pancytopenia in 1, hyperlipidemia in 24, proteinuria in 7 and oral aphthae in 12. SRL was discontinued in 4 patients and the reasons were refractory peripheral edema, severe lymphedema, severe hyperlipidemia and proteinuria> 1gr/d. In conclusion, Cs-A withdrawal and conversion to SRL was associated with improvement of renal function. No serious adverse effect was observed with SRL. SRL provides an alternative to Cs-A in maintenance immunosuppressive therapy after kidney transplantation. .