A 15-month-old girl was successfully treated for substantial hyperosmolarity in the absence of ketosis at the onset of permanent insulin-requiring diabetes mellitus. Hypotonic solutions containing small amounts of glucose and subcutaneous administration of low doses of insulin were employed. Potassium was added to the hydrating solutions during the second hour of treatment. In the next three months, two recurrences of this syndrome were verified and successfully treated in a similar manner.