Median (inter-quartile range) LOS was 8 (5-15) days and was higher in people with diabetes mellitus (adjusted time ratio 1.10, 95% CI 1.08-1.11, P<0.001).<h4>Conclusions</h4>People with diabetes mellitus undergoing colorectal resection are at a higher risk of 90-day mortality, prolonged LOS, and 90-day readmission, with use of insulin associated with additional risk. This evidence concerns the gene INS and diabetes mellitus.