BACKGROUND As an immunosuppressive treatment, cyclosporine carries a significant risk of nephrotoxicity. In this study, we assessed the safety and efficacy of sirolimus conversion in our kidney transplant recipients. METHODS Sirolimus conversion in 99 kidney transplant recipients was evaluated. Serum level of creatinine, glomerular filtration rate (GFR), and the occurrence of adverse effects of sirolimus were evaluated at conversion time and 1, 6, 12, 24, and 36 months after conversion. RESULTS The major causes of conversion were chronic allograft nephropathy and cyclosporine nephrotoxicity. The median time to conversion and follow-up were 54.7 months and 24 months, respectively. Three patients died during the study period. The acute rejection rate was 4%. In 16.6% of the patients, sirolimus was discontinued because of refractory adverse effects. No significant changes in estimated GFR and incidence of adverse effects were observed between patients with baseline estimated GFR lower or higher than 40 mL/min. Patients with early sirolimus conversion (less than 6 months after transplant) had improvement of their GFR (59.9 +/- 22.3 mL/min to 68.0 +/- 15.5 mL/min, P = .02), while kidney recipients with late conversion did not show such an improvement. The difference between GFRs in these two groups reached significant level at 12 months and stayed significant until the end of the follow-up. CONCLUSIONS This study emphasizes that conversion of cyclosporine to sirolimus could be associated with stable kidney allograft function. However, cyclosporine discontinuation should be considered early when it is indicated.