Clinical and laboratory data of 53 children with diabetes mellitus who were brought to Seoul National University Hoapital from Jan1967 to May, 1986 were analysedl 'retrospectively. The following results were obtained; 1) Patients were claseified as 50 cases of NIDDM and 3 cases of NIDDM. 2) Male to female. Ratio of Lddm was 1: 2.3 and mean age at onaet was 7 years old. 3) The number of newly disgnosed diabetic patients increased anually, especielly recently. 4) Seasonal variation at the onset of IDDM was remarkable with peak incidence in winter and early spring. 5) 22% of IDDM patients was accompanied by diabetic ketoacidosis at the onset of disease. 6) Total 34 episodes of ketoacidosis developed in 24 IDDM patients major presenting symptoms were abdominal pain, altered coneciousness vomlting, hyperventilation and generalized weakness. 7) The most frequent presumptive precipitating factor of ketoacidosis was discontiniance of insulin injection. 8) Laboratery findings at the ketoacidose were remarkable. 9) duriag followup period, the growth retardation was more marked in patients with higher HbA,c level, longer disease duration. 10) Major complications found during follow up period were diabetic ketoacidosis, infection ,lipodystrophy, hypoglycemia convulsion and cataract.