BackgroundHyperglycaemia is common in critically ill patients, but blood glucose and insulin management may differ widely among intensive care units (ICUs). We aimed to describe insulin use practices and the resulting glycaemic control in French ICUs. We conducted a multicentre 1-day observational study on November 23, 2021, in 69 French ICUs. Adult patients hospitalized for an acute organ failure, severe infection or post-operative care were included. Data were recorded from midnight to 11:59 p.m. the day of the study by 4-h periods.ResultsTwo ICUs declared to have no insulin protocol. There was a wide disparity in blood glucose targets between ICUs with 35 different target ranges recorded. In 893 included patients we collected 4823 blood glucose values whose distribution varied significantly across ICUs (P< 0.0001). We observed 1135 hyperglycaemias (> 1.8 g/L) in 402 (45.0%) patients, 35 hypoglycaemias (≤ 0.7 g/L) in 26 (2.9%) patients, and one instance of severe hypoglycaemia (≤ 0.4 g/L). Four hundred eight (45.7%) patients received either IV insulin (255 [62.5%]), subcutaneous (SC) insulin (126 [30.9%]), or both (27 [6.6%]). Among patients under protocolized intravenous (IV) insulin, 767/1681 (45.6%) of glycaemias were above the target range. Among patients receiving insulin, short- and long-acting SC insulin use were associated with higher counts of hyperglycaemias as assessed by multivariable negative binomial regression adjusted for the propensity to receive SC insulin: incidence rate ratio of 3.45 (95% confidence interval [CI] 2.97–4.00) (P< 0.0001) and 3.58 (95% CI 2.84–4.52) (P< 0.0001), respectively.ConclusionsPractices regarding blood glucose management varied widely among French ICUs. Administration of short or long-acting SC insulin was not unusual and associated with more frequent hyperglycaemia. The protocolized insulin algorithms used failed to prevent hyperglycaemic events.Graphical AbstractSupplementary InformationThe online version contains supplementary material available at 10.1186/s13613-023-01142-9.