The diabetic emergencies diabetic ketoacidosis (DKA), hyperglycemic hyperosmolar state (HHS) and hypoglycemia represent severe and potentially life-threatening complications of diabetes mellitus that require prompt diagnostics and treatment. Absolute or relative insulin insufficiency is characteristic of DKA und HHS along with severe dehydration. They differ by the prevalence of ketone bodies and the severity of acidosis; however, the treatment regimens are similar. In contrast, hypoglycemia is the limiting factor for achieving ambitious glucose targets. This article decribes the clinical presentation, diagnostics and emergency management of these metabolic derangements.