There is little data documenting cortisol levels in children with diabetic ketoacidosis (DKA), despite the fact that untreated adrenal insufficiency (AI) could worsen the outcome of DKA. In this cross-sectional study, we assessed serum cortisol levels in 28 children with DKA and new onset type 1 diabetes mellitus evaluated at our center over a 5-year period. Average duration of diabetes-related symptoms was positively associated with age (P = .002), and significantly lower hemoglobin A1c levels were observed in the youngest children. The mean cortisol level was 40.9 µg/dL, with a range of 7.8 to 119 µg/dL. Cortisol levels were found to be inversely associated with serum pH (P = .007). There was no difference in the clinical outcome of the 4 patients who had cortisol levels less than 18 µg/dL. Overall, we did not find clinical or laboratory evidence of diminished cortisol reserve; however, the possibility of AI must be kept in mind when treating children with DKA.