BACKGROUND: Type 1 diabetes mellitus is an autoimmune disease in which serum antibodies against islet antigens have been recognized. These antibodies include cytoplasmic islet cell antibodies (ICA), and glutamic acid decarboxylase (GAD)65 antibodies and IA2 antibodies. It has been reported that the prevalence of these autoantibodies is different among Caucacian and Asian and Korean type 1 diabetes patients. And the natural course of type 1 diabetes can differ according to the age of onset. But, in contrast to the classic juvenile onset type 1 diabetes, the adult onset type 1 diabetes is poorly characterized about clinical and autoimmune differences at presentation. Thus, this study was perfomed to evaluate clinical and autoimmune characteristics at presentation in subjects with either child onset or adult onset type 1 diabetes and to establish an autoimmune pathogenesis in Korean type 1 diabetes. METHOD: We examined the clinical characteristics of child onset type 1 diabetes (n=32) and adult onset type 1 diabetes (n=40) retrospectively. At the same time, ICA from these patients was measured by standard indirect immunofluorescence, GADA and IA2A from these patients were measured by radioimmunoassay. RESULTS: The mean duration of disease was longer in the adult onset and their serum fasting C-peptide concentration at diagnosis were higer. The prevalence of ICA, GADA, IA2A in sera from 32 patients with child onset type 1 diabetes was 50%, 38% and 31% respectively. And, the prevalence of ICA, GADA and IA2A in sera from 40 patients with adult onset type 1 diabetes was 30%, 25% and 18% respectively.The prevalence of ICA, GADA and IA2A in sera from 39 patients with typical type 1 diabetes was 46%, 30% and 16% respectively. And, the prevalence of ICA, GADA and IA2A in sera from 33 patients with atypical type 1 diabetes was 30%, 30% and 25% respectively. The concordance rate of ICA and GADA in child onset and adult onset diabetes was 81% (26/32), 80% (32/40) respectively. In a subset of these patients with recent onset type 1 diabetes (duration of diabetes < or = 1 year), the prevalence of ICA, GADA and IA2A was 75% (3/4), 75% (3/4), 100% (1/1) respectively, in the child onset type 1 diabetes. CONCLUSION: These observations show that autoantibodies in Korean patients with child onset type 1 diabetes is similar compaired with other Asian groups but is lower than Caucasian patients with type 1 diabetes and the prevalence of humoral immunologic makers in child onset type 1 diabetes was higher than that of adult onset diabetes. These results suggest that autoimmune response is a significant cause of Korean type 1 diabetes but other factors except autoimmunity may play an important role in the pathogenesis of Korean type 1 diabetes.