This single arm study will assess the efficacy and safety of Mircera when administered once monthly, subcutaneously or intravenously, for the maintenance of hemoglobin levels in dialysis patients with chronic renal anemia. Patients currently receiving maintenance treatment with epoetin alfa will receive monthly injections of Mircera with a starting dose (120, 200 or 360 micrograms) derived from the dose of epoetin alfa they were receiving in the week preceding study start. The anticipated time on study treatment is 3-12 months, and the target sample size is 100-500 individuals.