Introduction: Glycaemic control has been associated with improvement in morbidity and mortality in critically ill patients. However, the method of measuring blood glucose is crucial for insulin adjustment. Arterial blood glucometers are used widely in intensive care units, but there is a limited evidence base. Objective: To determine the correlation, accuracy, and agreement of blood glucose levels measured by the arterial blood glucometer versus standard venous blood glucose testing and identify the agreement of insulin dosage adjustment between the two methods. Method: Forty-five pairs of arterial and venous blood samples were obtained from 15 haemodynamically stable, critically ill patients. Pearson’s correlation coefficient and Clarke error grid analysis were used to identify the correlation and accuracy of the two methods, and Bland-Altman analysis to assess agreement. The Kappa statistic evaluated the agreement of insulin dosage adjustment between the two methods. Results: The arterial blood glucometer showed good correlation (r = 0.973), excellent accuracy, and good agreement with the central laboratory measurement of venous blood glucose. Agreement of the dosage adjustment of insulin infusion in the two groups was almost perfect (Kappa = 0.942). Conclusions: This study identified good correlation and excellent accuracy, and satisfactory agreement of blood glucose measured by the arterial glucometer and standard venous measurement. There was an almost perfect agreement of insulin dosage adjustment by arterial glucometer compared with venous blood. A glucometer for arterial blood glucose and insulin adjustment has evidence-based support. © 2016, Netherlands Society of Intensive Care. All rights reserved.