Diabetic ketoacidosis is an acute complication of diabetes mellitus that can be life-threatening if not treated properly. Once thought to occur only in patients with type 1 diabetes, diabetic ketoacidosis has been also observed in patients with type 2 diabetes under certain conditions. The basic underlying mechanism for diabetic ketoacidosis is insulin deficiency coupled with elevated levels of counter-regulatory hormones, such as glucagon, cortisol, catecholamines, and growth hormone. Diabetic ketoacidosis can be the initial presentation of diabetes mellitus or precipitated in known diabetic patients by many factors, most commonly infection. The management of diabetic ketoacidosis involves careful clinical evaluation, correction of metabolic abnormalities, identification and treatment of precipitating and comorbid conditions, appropriate long-term treatment of diabetes, and plans to prevent recurrence. Certain areas need further research, such as indications for the use of bicarbonate and phosphates and the use of intravenous rapid-acting insulin.