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Introduction Colorectal cancer (CRC) is the third most common cancer and the fourth most common cause of cancer death. CRC is commonly associated with anaemia. There has been significant focus on the correction of preoperative anaemia to reduce autologous blood transfusion (ABT) which has been associated with cancer recurrence. However, there has been little focus on the patient’s postoperative cancer journey. Research has demonstrated postoperative anaemia to be associated with delirium, acute kidney injury, myocardial infarction and increased frailty. In CRC specifically postoperative anaemia has been associated with prolonged hospital stay and increased all-cause mortality.The aim is to investigate how treatment with intravenous iron (IVI) impacts on the presence and severity of postoperative anaemia. Our primary outcome is haemoglobin (Hb) postoperatively, our secondary outcomes are ABT, length of hospital stay, readmission, complications, receipt of chemotherapy and mortality.Methods A literature search was conducted using MEDLINE (Pubmed), Ovid Embase, and Cochrane Central Register of Controlled Trials up to November 2024. We included randomised control trials (RCTs) and cohort studies comparing the use of IVI in the perioperative period (pre or post operative) and a comparator, standard care, oral iron or placebo.Statistical analysis was performed using RevMan 5.4. In instances where dichotomous outcomes were reported odds ratios (OR) with 95% confidence intervals (CI) were calculated. The mean difference with 95% CI was used for continuous outcomes. The Newcastle-Ottawa Scale (NOS) for cohort studies and Risk of Bias Tool 2 (RoB2) used in RCTs to assess the risk of bias.Results Sixteen studies, involving 2,671 patients were included in our analysis. We found a statistically significant increase in Hb at discharge in patients who received preoperative IVI: MD 0.39 (0.08, 0.70) p=0.01 and increased Hb at follow up in patients treated pre or postoperatively: MD 0.62 (0.32, 0.92) p< 0.0001. We found fewer patients treated with IVI preoperatively required ABT: OR 0.62 (0.42, 0.92), p=0.02 and fewer units of blood were transfused: MD -0.33 (-0.65, -0.00) p=0.05. We did not show a significant effect on complications OR 0.89 (0.64, 1.24) p=0.49, receipt of chemotherapy OR1.03 (0.70, 1.52) p=0.87 or mortality OR 0.59 (0.30, 1.19) p=0.14. Using ROB2 the risk of bias was low in the RCTs and using NOS most cohort studies were found to be medium risk of bias.Conclusion Treatment of perioperative anaemia with IVI improves the Hb at follow up and reduces ABT in CRC patients. This meta-analysis demonstrates the IVI is effective in treating perioperative anaemia in CRC. The reduction in ABT suggests that there could be an impact on cancer recurrence and mortality, but further work is need in this area.