Objective: The international guidelines for the treatment of diabetic ketoacidosis (DKA) advise against rapid changes in osmolarity and glucose; however, the optimal rates of correction are unknown. We aimed to evaluate the rates of change in tonicity and glucose level in intensive care patients with DKA and their relationship with mortality and altered mental status. Methods: This is an observational cohort study using 2 publicly available databases of U.S. intensive care patients (Medical Information Mart for Intensive Care-IV and Electronic Intensive Care Unit), evaluating adults with DKA and associated hyperosmolarity (baseline Osm ≥300 mOsm/L). The primary outcome was hospital mortality. The secondary neurologic outcome used a composite of diagnosed cerebral edema or Glasgow Coma Scale score of ≤12. Multivariable regression models were used to control for confounding factors. Results: On adjusted analysis, patients who underwent the most rapid correction of up to approximately 3 mmol/L/hour in tonicity had reduced mortality (n = 2307; odds ratio [OR], 0.21; overall P < .001) and adverse neurologic outcomes (OR, 0.44; P < .001). Faster correction of glucose levels up to 5 mmol/L/hour (90 mg/dL/hour) was associated with improvements in mortality (n = 2361; OR, 0.24; P = .020) and adverse neurologic events (OR, 0.52; P = .046). The number of patients corrected significantly faster than these rates was low. A maximal hourly rate of correction between 2 and 5 mmol/L for tonicity was associated with the lowest mortality rate on adjusted analysis. Conclusion: Based on large-volume observational data, relatively rapid correction of tonicity and glucose level was associated with lower mortality and more favorable neurologic outcomes. Avoiding a maximum hourly rate of correction of tonicity >5 mmol/L may be advisable.