OBJECTIVE: To evaluate the effectiveness of routine intravenous iron in surgical patients with iron deficiency anemia (IDA). BACKGROUND: Anemia is the most common medical disease in the world and is an independent risk factor for morbidity and mortality. Iron deficiency (ID) is the main cause for anemia and constitutes a potentially preventable condition with great impact on surgical outcome. METHODS: In this prospective single-center observational study, surgical patients were screened for the presence of anemia and ID. Patients were assigned to 1 of 4 study groups: A- (no anemia); A-, ID+, T+ (no anemia, iron-deficient, iron supplementation); A+ (anemia); and A+, ID+, T+ (anemia, iron-deficient, iron supplementation) according to hemoglobin level, iron status, and supplementation with iron. RESULTS: Among 1728 patients, 1028 were assigned to A-; 55 to A-, ID+, T+; 461 to A+; and 184 to A+, ID+, T+. While all iron-supplemented IDA patients required less red blood cell (RBC) transfusion during the postoperative period (A+ 42.5% vs A+, ID+, T+ 31.5%), a reduced intraoperative transfusion rate was observed for ID and IDA patients only if iron was supplemented >7 days before surgery. Hospital stay was significantly reduced by 2.8 days in iron-supplemented patients (P < 0.01 comparing 13.9 ± 0.8 days for A+, ID+, T+ vs. 16.7 ± 0.7 days for A+). CONCLUSION: Preoperative IDA management with intravenous iron is effective in improving hemoglobin level, thereby reducing intraoperative RBC transfusion rate particular if iron is administrated >7 days before surgery. Hospital length of stay was reduced in all preoperatively iron-supplemented IDA patients.