The objective of the present study was to determine the prevalence of autoimmune thyroid disease in Indian children with type 1 diabetes mellitus by the assay of antibodies to thyroid peroxidase and thyroglobulin. The study population consisted of 35 children with type 1 diabetes mellitus and 32 healthy age- and sex-matched control children. Thyroid peroxidase antibodies (TPO) were determined by ELISA and thyroglobulin antibodies (TGA) by passive hemagglutination. Thyroid function tests and tests of glycemic control were also performed. These assays were repeated after six months and one year. TPO were observed in 19 (54.3%) patients compared to three (10%) controls, and TGA in 11 (31.4%) patients and none of the controls. Both these observations were statistically significant with p=0.0002 for TPO and 0.0016 for TGA. The prevalence of these antibodies was not different in boys and girls and did not change with the duration of diabetes. All patients who were positive for TGA were also positive for TPO. Thyroid function tests were abnormal in one patient who was found to have Hashimoto's thyroiditis. There is a definite need to screen all diabetic children for thyroid antibodies and carefully follow up those patients in whom these antibodies are positive.