The diabetic hypersomolar state is defined by a serum glucose greater than 600 mg/dl and a serum osmolarity greater than 320 m Osm/L. Ketoacidosis or lactic acidosis may co-exist with DHS in the same patient. The incidence of this acute complication of diabetes is high enough (17.5 cases per 100,000 person-years) for primary care physicians to encounter a case every year or two. Predisposing factors include older age, female sex, nursing home residence, and infection. A substantial proportion of cases occur in patients with no prior history of diabetes. Common presenting signs include fatigue or weakness, polydipsia, polyuria, nausea, and alteration of consciousness. The mainstay of therapy is intravenous fluid replacement with close monitoring of glucose and electrolytes in a hospital setting. Current mortality figures are high, at 10% to 20%, and the chance of survival is adversely affected by older age, higher osmolarity, and the presence of an associated severe illness. Prevention includes screening for diabetes, educating diabetic patients and their care givers about the symptoms of hyperglycemia, prompt treatment of any infection in a diabetic person, avoidance of drugs that increase carbohydrate intolerance in diabetic people, and encouraging compliance with treatment of diabetes.