The case of five pediatric patients who presented to the Royal Children's Hospital, Melbourne with newly diagnosed diabetes mellitus between January 2001 and September 2003 is reported. Each case was complicated by hyperosmolarity and hypernatremia and required intensive therapy. Fluid intake prior to admission in each case was documented and consisted of between 5 and 12 L of carbonated carbohydrate beverages and 'isotonic' sports drinks. At presentation, biochemical results of the four cases (four males and one female), mean age 13.6 yr (range 11.7-15.1 yr) included glucose (mean 1460 mg/dL; range 864-2106), adjusted sodium (mean 176.3 mmol/L; range 165-183), serum osmolarity (mean 399 mmol/kg; range 364-424), anion gap (mean 48 mEq/L; range 42-84), and pH (mean 7.15; range 7.01-7.27). All five cases had evidence of ketonuria on presentation. Treatment in all five cases consisted of replacement of fluids over a prolonged period of 72 h and careful monitoring of electrolyte response. Three of five cases required hemofiltration in the first 48 h postadmission. All five cases made a complete recovery without neurological sequelae. Carbonated carbohydrate fluid intake may precipitate a more severe presentation of type 1 diabetes mellitus (T1DM). Fluid composition and intake should be carefully estimated at admission to help identify and manage similar cases.