Background and aim of the study: Patients with iron deficiency (ID) who are unable to tolerate or show sub-optimal response to oral iron therapy are candidates for parenteral iron therapy. This study evaluated the patient safety and tolerance of iron polymaltose given either as a 2-hour infusion or as a 4-hour infusion. Methods: A total of 243 patients with ID were randomized alternatively to receive iron polymaltose infusion either as a 2-hour infusion or as a 4-hour infusion. All patients received pre-medication with certizine hydrochloride 10 mg PO one-hour before infusion and hydrocortisone 50 mg IVI immediately before infusion. Infusion related adverse events/side-effects during the infusion and over the next seven days were documented and graded as mild, moderate or severe. Results: The age of the patients ranged from 17 years to 92 years (mean 55.5 yr); M:F = 1:3.5. One hundred and twenty-two patients were in the 2-hour arm (M:F = 1:5; mean age 52.9 yr) and 121 were in the 4-hour arm (M:F = 1:2.6; mean age 58.1 yr). Iron infusion therapy was generally well tolerated by patients in both arms. Adverse events/side effects were documented in 14 patients in each arm (22 events in the 2-hour arm and 20 in the 4-hour arm) and included aches and pains, cannula-site pain/swelling, nausea, abdominal cramps, rash, vagal response, metallic taste, hot flushes and headaches. In most patients, these events were mild and none had any severe events. Conclusion: The incidence of adverse events with 2-hour infusion of iron polymaltose is similar to that observed with 4-hour infusion of iron polymaltose.