Ascertain the Optimal Starting Dose of Mircera Given Subcutaneously for Maintenance Treatment of Anemia in Pediatric Patients With Chronic Kidney Disease on Dialysis or Not Yet on Dialysis.

Inclusion Criteria: * Pediatric participants 3 months to 17 years of age with clinically stable chronic renal anemia * CKD with estimated glomerular filtration rate (eGFR) of \< 45 mL/min/1.73 m2 (determined by the Bedside Schwartz formula) or dialysis treatment for at least 8 weeks before the first dose of Mircera * For participants on peritoneal dialysis (PD): a weekly Kt/V≥ 1.8 * For participants on hemodialysis (HD): adequate HD, urea reduction ratio (URR) \> 65% or Kt/V \> 1.2 for participants on HD three times per week. Participants with fewer than or more than three HD sessions per week should have a weekly Kt/V≥ 3.6. * Baseline Hb concentration 10.0-12.0 g/dL determined from the mean of two Hb values measured at Visit 1 (Week -3) and Visit 2 (Week -1) * Stable SC maintenance treatment with epoetin alfa, epoetin beta, or darbepoetin alfa with the same dosing interval for at least 6 weeks before the first dose of Mircera * Stable dose of epoetin alfa, epoetin beta, or darbepoetin alfa treatment with no weekly dose change \> 25% (increase or decrease) for at least 4 weeks before the first dose of Mircera * Adequate iron status defined as ferritin≥100 ng/mL or transferrin saturation (TSAT)≥ 20% (or percentage of hypochromic red cells \< 10%); mean of two values measured during screening. Exclusion Criteria: * Overt gastrointestinal bleeding within 8 weeks before screening or during the screening period * RBC transfusions within 8 weeks before screening or during the screening period * Hemoglobinopathies (e.g., homozygous sickle-cell disease, thalassemia of all types) Hemolytic anemia, Active malignant disease * PD subjects with an episode of peritonitis within the past 30 days prior to screening and/or during the screening period * Uncontrolled or symptomatic inflammatory disease (e.g., systemic lupus erythematosus) * Uncontrolled hypertension as assessed by the investigator * Epileptic seizures within 3 months prior to screening and during the screening period * Administration of any investigational drug within 4 weeks prior to screening or planned during the study * Severe hyperparathyroidism (intact parathyroid hormone \[PTH\]≥ 1000 pg/mL or whole PTH≥ 500 pg/mL) or biopsy-proven bone marrow fibrosis * Kidney transplant with use of immunosuppressive therapies known to exacerbate anemia * Known hypersensitivity to recombinant human erythropoietin (EPO), polyethylene glycol, or any constituent of the study drug formulation * Anti-EPO antibody (AEAB)-mediated pure red cell aplasia (PRCA) or history of AEAB mediated PRCA or positive AEAB test result in the absence of PRCA * High likelihood of early withdrawal or interruption of the study (e.g., planned living donor kidney transplant within 5 months of study start) * Planned elective surgery during the entire study period