Iron supplementation is required in a preponderance of peritoneal dialysis (PD) patients treated with erythropoietic stimulatory agents (ESAs). Although many authors and clinical practice guidelines recommend primary oral iron supplementation in ESA-treated PD patients, numerous studies have clearly demonstrated that, because of a combination of poor bioavailability of oral iron, gastrointestinal intolerance, and noncompliance, oral iron supplementation is insufficient for maintaining a positive iron balance in these patients over time. Controlled trials have demonstrated that, in iron-deficient and iron-replete PD patients alike, intravenous (IV) iron supplementation results in superior iron stores and hemoglobin levels with fewer side effects than oral iron produces. Careful monitoring of iron stores in patients receiving IV iron supplementation is important in view of conflicting epidemiologic links between IV iron loading and infection and cardiovascular disease. Emerging new iron therapies such as heme iron polypeptide and ferumoxytol may further enhance the tolerability, efficacy, and ease of administration of iron in PD patients.