We present a case of a 47-year-old man with Type 2 diabetes mellitus who attempted suicide with 2,100 U of insulin injected subcutaneously. Administration of dextrose intravenously was required to maintain the blood glucose concentration normally for 5 days. Moreover, hypokalemia, hypophosphatemia, and hypomagnesemia were also seen for 24 hours after insulin injection. The serum phosphorus and magnesium concentrations decreased to nadirs of 1.6 mg/dl and 1.6 mg/dl respectively 7 hours after insulin injection. Electrolyte disorders other than hypokalemia may be induced in hypoglycemic patients by massive insulin overdose.