Study to Evaluate Safety and Efficacy of Early Calcineurin Inhibitor Withdrawal in Primary Renal Allografts

Inclusion Criteria: * Male and female patients between 18 and 75 years of age. * Patients who are 90 to 240 days after having received a primary living or cadaver renal allograft. * Patients maintained on a regimen of cyclosporine or tacrolimus and MMF since transplantation. * Capable of providing written informed consent. * No known contraindications to treatment with sirolimus. Exclusion Criteria: * Pregnant or lactating. * Acute rejection within 90 days prior to study randomization. * More than one biopsy proven acute rejection episode prior to study randomization. * Previously received or are receiving an organ transplant other than kidney. * Receiving sirolimus prior to entry. * Severe diarrhea or other gastrointestinal disorders that may interfere with their ability to absorb oral medication. * Evidence of active systemic infection requiring antibiotics, or HIV, HCV, HBV infection. * History of malignancy in the past 5 years. * Require dialysis at the time of study entry.