Decompensated hyperglycemia is a frequent, severe complication of diabetes mellitus. Ketoacidosis usually occurs in patients with insulin-dependent (type I) diabetes, and insulin therapy is required to correct their hyperglycemic derangement. Hyperosmolar nonketotic state is more common in patients with non-insulin- dependent (type II) diabetes, who usually present with severe dehydration and hyperosmolar plasma. They respond readily to aggressive volume expansion, and insulin has a lesser role in management. Some patients exhibit a mix ture of ketoacidosis and hyperosmolarity, which suggests that the two conditions may represent variants of decompensated by the magnitude of dehydration and the severity of acidosis. All diabetic patients with hyperglycemic decompensation should return to their usual hypoglycemic programs as soon as possible and receive close follow-up after hospitalization.