Unlike calcineurin inhibitors, sirolimus is devoid of significant nephrotoxicity. We aimed to report our experience with conversion to sirolimus in patients with chronic allograft nephropathy at our transplant center. Since 1985, 1385 renal transplantation were performed at our center. Among them, calcineurin inhibitor was converted to sirolimus in 88 patients because of biopsy proven chronic allograft nephropathy, calcineurin inhibitor toxicity, or other calcineurin inhibitor adverse effects, which were analyzed retrospectively. Patients were divided into 2 groups: group 1 (conversion to sirolimus at creatinine levels < 2 mg/dL) and group 2 (conversion to sirolimus at creatinine levels > 2 mg/dL). Eighty-eight renal transplant patients (64 men, 24 women; mean age, 35.9 ± 9.9 years; age range, 21-59 years) with biopsy proven chronic allograft nephropathy, calcineurin inhibitor toxicity, calcineurin inhibitor adverse effects, or persistence of malignancy were converted to sirolimus. At the time of conversion, the mean duration of transplant was 48±15 months (range, 4-296 months). Before conversion, immunosuppressive treatment had consisted of a calcineurin inhibitor + prednisolone + mycophenolate mofetil. After conversion, the calcineurin inhibitor was stopped and sirolimus was started. In group 2, 49 patients underwent conversion; the mean serum creatinine level increased to 3.2±1.4 mg/dL. In this group, 17 patients rejected the transplant. In group 1, 40 patients underwent conversion; the mean serum creatinine level fell to 1.4±0.5 mg/dL for only 3 patients. In conclusion; calcineurin inhibitor toxicity can lead to chronic allograft nephropathy. Stabilizing kidney function can be done in patients with a low baseline serum creatinine level. Late conversion to sirolimus may result in graft failure. If therapy without a calcineurin inhibitor is considered, it should be initiated before the serum creatinine level rises to 2 mg/dL.