ABSTRACT Islet cell autoantibodies are early markers for type 1 diabetes. The aim of this study was to determine whether islet autoantibodies were present at birth in young adults who developed type 1 diabetes at 15-30 years of age. Cord blood sera from 30 patients who developed type 1 diabetes between 15 and 25 years of age and sera from 320 randomly selected control children were tested for islet cell antibodies (ICA) by indirect immunofluorescence and autoantibodies against the 65 kD isoform of glutamic acid decarboxylase (GADA), islet cell antigen-2 (IA-2A) and insulin (IAA) by radiobinding assays. The young adults who developed type 1 diabetes did not differ from controls in the cord blood prevalence of any of the four islet autoantibodies. This is in contrast to our previous findings that children who developed type 1 diabetes below 15 years of age had an increased prevalence of cord blood islet autoantibodies. Our present data suggest that, in contrast to children, pre- and perinatal risk factors are less likely to be involved in the development of type 1 diabetes in young adults.