Patient Blood Management (PBM) is an evidence-based, multidisciplinary, patient-centred approach to optimizing the care of patients who might need a blood transfusion. This systematic review aimed to collect the best available evidence on the effectiveness of preoperative iron supplementation with or without erythropoiesis-stimulating agents (ESAs) on red blood cell (RBC) utilization in all-cause anaemic patients scheduled for elective surgery. Five databases and two trial registries were screened. Primary outcomes were the number of patients and the number of RBC units transfused. Effect estimates were synthesized by conducting meta-analyses. GRADE (Grades of Recommendation, Assessment, Development and Evaluation) was used to assess the certainty of evidence. We identified 29 randomized controlled trials (RCTs) and 2 non-RCTs comparing the effectiveness of preoperative iron monotherapy, or iron + ESAs, to control (no treatment, usual care, placebo). We found that: (1) IV and/or oral iron monotherapy may not result in a reduced number of units transfused and IV iron may not reduce the number of patients transfused (low-certainty evidence); (2) uncertainty exists whether the administration route of iron therapy (IV vs oral) differentially affects RBC utilization (very low-certainty evidence); (3) IV ferric carboxymaltose monotherapy may not result in a different number of patients transfused compared to IV iron sucrose monotherapy (low-certainty evidence); (4) oral iron + ESAs probably results in a reduced number of patients transfused and number of units transfused (moderate-certainty evidence); (5) IV iron + ESAs may result in a reduced number of patients transfused (low-certainty evidence); (6) oral and/or IV iron + ESAs probably results in a reduced number of RBC units transfused in transfused patients (moderate-certainty evidence); (7) uncertainty exists about the effect of oral and/or IV iron + ESAs on the number of patients requiring transfusion of multiple units (very low-certainty evidence). Effect estimates of different haematological parameters and length of stay were synthesized as secondary outcomes. In conclusion, in patients with anaemia of any cause scheduled for elective surgery, the preoperative administration of iron monotherapy may not result in a reduced number of patients or units transfused (low-certainty evidence). Iron supplementation in addition to ESAs probably results in a reduced RBC utilization (moderate-certainty evidence).