Severe hypertriglyceridemia exceeding 5.6 mmol/L in diabetic ketoacidosis occasionally occur in patients with type 1 diabetes mellitus. The pattern of dyslipidemia is usually Fredrickson classification type lV. But it also exists in type III and type V. However, extreme triglyceridemia, triglyceride level exceeds 22.6 mmol/L, occur rarely in the modern era of insulin therapy. And the pattern is usually Fredrickson type I. The severe hypertriglyceridemia in diabetic ketoacidosis is mainly due to lipoprotein lipase deficiency, and secondly to insulin deficiency. The severity usually improves with insulin replacement. In patients with extreme hypertriglyceri-demia, serum electrolyte values of the patients are fallaciously low, and it leads to the misinterpretation of biochemical results and to the inappropriate treatment. We reported a case of a 25 years old female patient with diabetic ketoacidosis and extreme hypertriglyceridemia. At admission, the color of her serum was milky, her plasma triglyceride concentration was 144.7 mmol/L (12864 mg/dL), cholesterol was 25.5 mmol/L (982 mg/dl), and HDL-cholesterol was 0.77 mmol/L (40 mg/dL). The biochemical values at admission could not be measured. Empirical therapy was administered with the use of insulin and fluid. After the initial treatment with insulin and fluid, plasma triglyceride declined rapidly and was nearly normal after 72 hours. We also measured fasting blood glucose concentration and lipid profiles from her father and two sisters. Their plasma glucose and lipid profiles were normal.