Inclusion Criteria:

• All male or female patients aged less than 17 years.
• The patient has undergone a kidney transplant, from a cadaveric or living donor with compatible ABO blood type.
• The patient is more than 12 months post-transplantation.
• The allograft demonstrates histological changes consistent with CAN according to the Banff 97 classification schema (minimum of ct1 and ci1 score for tubular atrophy and interstitial fibrosis respectively).

Exclusion Criteria:

• The patient, or in case the patient is minor, the patient's parent(s) or their legal representative, has been fully informed and will not give informed consent to participate in the study.
• The allograft demonstrates histological changes at the time of enrollment consistent with acute allograft rejection Grade Ia or worse, according to the Banff 97 classification schema (minimum of t2 and i2 score for tubulitis and interstitial inflammation respectively).
• The patient is known to be allergic or intolerant to MMF, sirolimus or any of their known metabolites.
• The patient for who routine protocol kidney biopsy is contraindicated.
• Patients whose maintenance immunosuppression does not include both tacrolimus and prednisone at the time on study enrollment.
• Patients previously treated with sirolimus.
• The patient requires ongoing dosing with a systemic immunosuppressive drug at study entry for any reason other than kidney transplantation.
• The patient and/or donor is known to be HIV or HCV positive.
• The patient has significant liver disease, defined as having during the past 28 days continuously elevated ASAT (SGOT) and/or ALAT (SGPT) levels greater than 3 times the upper value of the normal range of the investigational site.
• The patient has persistent leukopenia (WBC <3.0 x109/L).
• The patient has persistent thrombocytopenia (<100 x109/L).
• The patient has pre-existing significant hyperlipidemia (total cholesterol >7.8 mmol/L), not responding to medical therapy.
• The patient has pre-existing elevated triglycerides, not responding to medical therapy.
• The patient with malignancy or history of malignancy except for successfully treated Wilm's tumor (2 years) or non-metastatic basal or squamous cell carcinoma of the skin that has been treated successfully.
• The patient has significant, uncontrolled concomitant infections and/or severe diarrhea, vomiting or active peptic ulcer.
• The patient has previously received or is receiving an organ transplant other than kidney.
• The patient is taking or has been taking an investigational drug in the past 28 days or is currently participating in another clinical intervention trial.
• Patients with the relapsing, non-diarrheal form of haemolytic-uraemic syndrome.
• The patient is unlikely to comply with the protocol.
• The patient has any form of substance abuse, psychiatric disorder or condition which, in the opinion of the investigator, may invalidate communication with the investigator
• Sexually active female patients who are pregnant or lactating or who do not consent to effective birth control.
• The patient is less than 6 years of age.
• The patient has significant and persistent EBV activity as measured by PCR amplification from blood samples.
• The patient has a prior history of post-transplant lymphoproliferative disease.