The original criteria described for euglycaemic ketoacidosis (initial blood glucose less than 16.7 mmol/l and plasma bicarbonate equal to or less than 10 mmol/l) were identified in 23 of 722 consecutive episodes (3.2%) of diabetic ketoacidosis. True euglycaemic ketoacidosis (initial blood glucose 10 mmol/l or less) was rare, occurring in 0.8-1.1% of all episodes depending on the defining plasma bicarbonate concentration. Management of euglycaemic ketoacidosis with low-dose continuous intravenous infusion of insulin together with adequate fluid replacement was effective. The clinical and biochemical data did not support the concept of euglycaemic ketoacidosis as a separate entity. The importance of ketone testing rather than glucose testing in the diagnosis of ketoacidosis is, however, emphasized. The importance of adequate insulin and fluid therapy in those few episodes where blood glucose is normal or near normal at presentation is also highlighted.