Hyperglycemia and other metabolic derangements resulting from absolute or functional deficiency of insulin are accompanied by typical signs and symptoms of diabetes. The clinical signs and the findings of hyperglycemia over 200 mg/dl should establish a diagnosis of diabetes mellitus. An oral glucose tolerance test (O-GTT) is rarely necessary for diagnosis of diabetes in a child. A small proportion of children, however, present less severe symptoms, and may require an O-GTT. Approximately 14% of IDDM children were in coma at diagnosis in Tokyo, and 11 onset deaths (0.94%) were observed among the 1172 newly diagnosed IDDM cases in Japan. A significant decline in the onset mortality, however, has been observed in the past 20 years in Japan in association with the improvement of early management of childhood diabetes. The clinical distinction of IDDM from NIDDM is often difficult in diabetic children of Oriental origin without obesity. Japanese IDDM can be divided into two forms, abrupt and slow onset forms, but they may be essentially the same disease. There was no difference in the frequency of being tested positive for circulating ICA between the two groups of the patients. But a difference in the frequency of HLA DR4 and DRW9 was noticed between the two groups. Clinical features of 107 children with NIDDM were studied and about 75% of these cases were obese. All of them can be detected by routine urinalysis for glucose. Diet and exercise therapy in most of the newly diagnosed patients resulted in remission but some of them may require insulin or an oral hypoglycemic agent to get better glycemic control.