Aims: The prevalence of islet cell, thyroid, adrenal and celiac disease related autoantibodies in patients with Type 1 diabetes mellitus (Type 1 DM) from Sri Lanka is described. Design and Methods: Autoantibodies to glutamic acid decarboxylase 65 (GAD65Ab), protein tyrosine phosphatase IA-2 (IA-2Ab), insulin (IAAb), thyroglobulin (TgAb), thyroid peroxidase (TPOAb), TSH receptor (TRAb), 21-hydroxylase (21-OHAb) and tissue transglutaminase (tTGAb) were measured in 122 Type 1 DM patients who had low C-peptide activity or were >20 yr old at the time of diagnosis and in 100 non-diabetic blood donors. Results: GAD65Ab and/or IA-2Ab were present in 74/122 (60.7%) Type 1 DM subjects with a significantly higher prevalence compared to non-diabetic controls (no. 100) (GAD65Ab-59 vs 4%; IA-2Ab-14 vs 0%; respectively) (p<0.001). The median (inter-quartile range) Type 1 DM duration in …