Background: The incidence of surgical site infection (SSI) in colorectal surgery (CRS) is higher than other forms of general surgery. Post-operative hyperglycaemia causes increased SSI in CRS. Post-operative hyperglycaemia control in cardiac surgery reduces SSI. The aim was to evaluate using a cohort comparison the effect of post-operative glycaemic control using an insulin infusion on SSI in CRS. Methods: Collection of data for the ACS-NSQIP was commenced in 2015. The CRS unit added post-operative glycaemic control to the SSI bundle in late 2016. The intervention was an insulin infusion to titrate blood glucose between 135 and 180 mg/Dl (7.5 and 10 mmol/l). The effect of glycaemic control on SSI was assessed comparing ACS-NSQIP raw data prior and after the intervention was commenced. Results: The NSQIP data from July 2015 to June 2016 revealed the incidence of SSI were 25%. From January 2017 to December 2017, there was a significant reduction in SSI to 6.1% (OR = 517 Cl = 1.92–16.08, p < 0.001). The incidence of organ/space SSI fell significantly from 13% to 1.0% (OR = 11.35, Cl = 1.62–488.7, p < 0.001). There was non-significant reduction in superficial SSI from 11 to 4.0% (OR = 2.93, Cl = 0.68–13.03, p = 0.06). There was no significant difference in other factors associated with SSI in CRS. Conclusion: Post-operative glycaemic control in CRS reduces the rate of SSI. Post-operative glycaemic control should be included in SSI bundles for CRS and may be of benefit in other surgical specialties. [ABSTRACT FROM AUTHOR]