Epoetin has been used to treat patients with renal anemia since 1988. -Anti-erythropoietin antibody-mediated pure red cell aplasia (PRCA) has been associated with epoetin usage, and a PRCA incidence of 4.5 per 10,000 patient-years was observed for epoetin-α (Eprex) in 2002. The PASCO II study (post-authorization safety cohort observation of Retacrit and Silapo (epoetin-ζ) administered subcutaneously for the treatment of renal anemia) followed 6,346 patients (4,501 Retacrit (group R); 1,845 Silapo (group S)) for up to 3 years of subcutaneous treatment with the biosimilar epoetin-ζ. One PRCA in 1 (0.02%) patient in group R who tested positive for neutralizing antibodies was reported. Overall, 527 adverse events of special interest (AESI) including PRCA occurred in 418 (6.60%) patients, lack of efficacy occurred in 34 (0.54%), and thromboembolic events in 389 (6.14%) patients. 41 adverse drug reactions other than AESIs were reported in 28 (0.44%) patients. The exposure-adjusted incident rate of PRCA was 0.84 per 10,000 patient-years. This real-world study showed that among patients with renal anemia receiving subcutaneous administration of the biosimilar product epoetin-ζ, the incidence rate of PRCA was substantially below the risk observed in 2002 for Eprex and that there was no immunogenicity concern or other new safety concern.