Prior studies have suggested an association between prolonged QT interval corrected for heart rate (QTc) and various ketotic conditions, such as diabetic ketoacidosis (DKA), ketogenic diets, and very-low-carbohydrate, calorie-restricted diets. This study assessed the QTc in 30 children during acute and after recovery from DKA. Nearly half (47%) of the children had a prolonged QTc during DKA, and 4 had persistently prolonged QTc during recovery. The QTc correlated with the anion gap during DKA, but not with the serum potassium, calcium, or magnesium levels. Cardiac monitoring during ketosis is warranted to avoid fatal arrhythmia.