We assessed the performance of the factory-calibrated, sixth-generation continuous glucose monitoring (CGM) system Dexcom G6® (DexCom Inc., San Diego, California) during elective abdominal surgery. Twenty adults with (pre)diabetes undergoing abdominal surgery (>2 hours; 15 men, age 69 ± 13 years, glycated haemoglobin 53 ± 14 mmol/mol) wore the sensor from 1 week prior to surgery until hospital discharge. From induction of anaesthesia until 2 hours post-surgery, reference capillary glucose values were obtained every 20 minutes using the Accu-Chek® Inform II meter (Roche Diabetes Care, Mannheim, Germany). The primary endpoint was the mean absolute relative difference (ARD) between sensor and reference method during this period. In total, 1207 CGM/reference pairs were obtained. In the peri-operative period (523 pairs), mean ± SD and median (interquartile range [IQR]) ARD were 12.7% ± 8.7% and 9.9 (6.3;15.9)%, respectively, and 67.4% of sensor readings were within International Organization of Standardization 15197:2013 limits. CGM overestimated reference glucose by 1.1 ± 0.8 mmol/L (95% limits of agreement -0.5;2.7 mmol/L). Clarke error grid zones A or B contained 99.2% of pairs (A: 78.8%; B: 20.4%). The median (IQR) peri-operative sensor availability was 98.6 (95.9;100.0)%. No clinically significant adverse events occurred. In conclusion, the Dexcom G6 device showed consistent and acceptable accuracy during elective abdominal surgery, opening new avenues for peri-operative glucose management.