The aim of this study was to evaluate the feasibility of a steroid-free maintenance immunosuppression regimen in long-term renal transplant (KTx) recipients after addition of sirolimus (SRL) to cyclosporine (CsA)-based immunosuppression. A multicenter, prospective pilot study of steroid withdrawal (SW) was initiated for KTx patients. SW was divided into three phases: (A) conversion to a SRL + CsA + steroid regimen; (B) steroid tapering and withdrawal; and (C) maintenance with SRL + CsA. Primary endpoints of the study were incidence of acute biopsy-proven rejection (AR) and safety. In the A and B phases of the study 42 KTx patients (132 +/- 75 months post-Tx) were entered into the study, 18 of 42 (43%) with severe, acute side effects due to the CsA + SRL combination. These side effects were reversible with reduction of CsA or with suspension of the SRL/CsA combination. An amendment was introduced in the protocol to drastically reduce the CsA exposure to <50 ng/mL (trough) at the time of SRL addition. After this amendment, 39 other KTx patients entered the study and only 3 of 39 (8%) were discontinued because of toxic side effects. In the overall cohort of 81 KTx patients, the incidence of AR after SW was low (n = 5, 6.1%), all occurring within the first 3 months after SW. These findings indicate: (1) addition of SRL to very low-maintenance CyA exposure allows safe SW in KTx; (2) with the SRL + CsA combination, the incidence of AR after SW is low in long-term KTx patients; and (3) in the first 3 months after SW strict monitoring for early diagnosis and treatment of AR is mandatory.