The term latent autoimmune diabetes in adults(LADA) was introduced to define adult diabetic patients who initially do not require insulin, but they have the immune markers of type 1 diabetes and in a number of cases, these patients progress to insulin dependency. LADA patients have several features of classic type 1 diabetes in addition to islet cell antibody positivity, including high rates of HLA-DR3 and DR4. We describe here a case of a patient with a diagnosis of LADA who, having been diagnosed with type 2 diabetes, was affected with diabetic ketoacidosis. In April 2000, a 65-year-old man was admitted to Chung-Ang University Hospital due to his decreased cognitive ability. The patient was diagnosed with type 2 diabetes 30-years ago and he was diagnosed 6-month ago as being in a hyperglycemic hyperosmolar state. He was positive for antibodies against GAD(anti-GAD, 31U/mL). His weight was 70kg, height 167cm, BMI 25 kg/m2 and the blood pressure was 86/52mmHg. No abnormalities on the physical examination were found. His acid-base balance was pH 6.937, serum bicarbonate 2.2mmol/L and the anion gap 38; he also had a strong positive reaction for ketones in his urine and serum. During half a year, the fasting C-peptide level decreased from 0.65nmol/L to 0.13nmol/L, which means the rapid progression of beta-cell destruction. Intensive treatment of LADA with insulin may improve this type of patients' quality of life, and so potentially save the beta-cell function and perhaps lessening the risk of a hyperglycemic crisis