Study objective: To evaluate the impact of intensive glucose control on diabetic patients undergoing surgery. Design: A systematic review and meta-analysis of randomized controlled trials. PubMed, CENTRAL, EMBASE, ISI Web of Science, and CINAHL databases were searched from inception to 13 December 2020. Setting: Operating room, postoperative recovery area and ward, up to 30 days after surgery. Patients: Diabetic patients undergoing surgery. Interventions: We used Review Manager 5.4 to pool the data with a random-effects model. The quality of evidence was rated using the Grading of Recommendations, Assessment, Development and Evaluation system. Measurements: The primary outcomes were infectious complications, postoperative mortality, and hypoglycaemia. The secondary outcomes included atrial fibrillation, myocardial infarction, stroke, delirium, renal failure, postoperative mechanical ventilation time, length of intensive care unit (ICU) stay, and hospital stay. Main results: Thirteen studies involving 1582 participants were included. Compared with conventional glucose control, intensive glucose control was associated with a lower risk of infectious complications (risk ratio [RR], 0.35; 95% confidence interval [CI], 0.19-0.63; low-quality evidence), atrial fibrillation (RR, 0.55; 95% CI, 0.42-0.71; high-quality evidence), and renal failure (RR, 0.38; 95% CI, 0.15-0.95; moderate-quality evidence), as well as a shorter length of stay in the ICU (mean difference (MD), -0.55 day; 95% CI, -1.05 to -0.05 days; very-low-quality evidence) and hospital (MD, -1.61 days; 95% CI, -2.78 to -0.44 days; very-low-quality evidence). However, intensive glucose control was associated with a higher risk of hypoglycaemia (RR, 3.00; 95% CI, 1.97-4.55; high-quality evidence). There were no significant differences in postoperative mortality, myocardial infarction, stroke, delirium, or postoperative mechanical ventilation time. Conclusions: Intensive glucose control in diabetic patients is associated with a reduction in some adverse postoperative outcomes including infectious complications, but also appears to increase the risk of hypoglycaemia. Further well-designed studies may be needed to determine appropriate regimens to reduce hypoglycaemia incidence. PROSPERO registration number: CRD42021226138.