Erythropoietic agents, a cornerstone of management, are a major component of the cost of renal replacement therapy. The objectives of this study were to compare (on a month-by-month basis) U.S. hemodialysis and peritoneal dialysis patients in terms of the proportion of patients receiving erythropoietin, erythropoietin doses, and hemoglobin levels after initiation of erythropoietin. Patients studied (hemodialysis, n = 121,970; peritoneal dialysis, n = 7129) began dialysis between 1995 and 2000, had Medicare as their primary payer, were 65 yr old or older at dialysis inception, had no erythropoietin claims before dialysis inception, and did not have a switch in dialysis modality in the first 6 mo of dialysis therapy. Total monthly erythropoietin doses and average monthly hemoglobin levels were calculated from Medicare claims. The proportion of patients who received erythropoietin plateaued at 3 mo in both groups: 25% in peritoneal dialysis patients and 80% in hemodialysis patients. However, monthly erythropoietin doses plateaued at 30,000 units in peritoneal dialysis patients and 60,000 units in hemodialysis patients, a disparity not explicable by differences in baseline characteristics. Among subjects who received erythropoietin, mean hemoglobin levels were similar at steady state in both populations and met the National Kidney Foundation Dialysis Outcomes Quality Initiative hemoglobin target level of 11 to 12 g/dl. Hemoglobin levels in U.S. hemodialysis and peritoneal populations are similar. However, erythropoietin doses are dramatically higher in hemodialysis patients.