Introduction Insulin dependent type 1diabetes (T1D) is a chronic inflammatory disorder characterized by the autoim¬mune destruction of pancreatic β cells. The autoim¬mune reaction is a multistep process triggered by interactions between immune cells and the islets (1) . Type 1 diabetes may be associated with additional autoimmune disorders including autoimmune thyroid disease (AITD) (2) , coeliac disease (3) , and Addison’s disease (4) . The pathogenetic mechanism underlying the simultaneous occurrence of these autoimmune diseases has not been clearly understood yet. Evidence exists that common genetic determinants– mainly human leukocyte antigen (HLA) risk alleles (5, 6) or other genes outside the HLA region (i.e., CTLA4 gene and PTPN22 gene) – could play a role (7, 8) .Moreover, environmental factors seem to be involved in the pathogenesis of these complex diseases (9) . The association between type I diabetes and AITD was first described in the early 1960s by Pettit, et al (10) and landing et al (11) .Several subsequent cross sectional studies from various parts of the world have shown regional and racial variation in the prevalence of thyroid antibodies (12,18) . The purpose of the present study was to evaluate the prevalence of antithyroid antibodies and thyroid dysfunction among diabetic and normal Sudanese children and to decide whether it is worth while screening the diabetic children as has been the recommended elsewhere (19) . Material and Methods Study design and area This is a cross sectional study conducted at the paediatric diabetic clinic of Jaber Abu Elez Diabetes Center, and Gaffar Ibn Oaf Children Hospital outpatient clinics, Khartoum State for one year. Subjects Sera were collected from 100 children and adolescents (55 boys, 45girls) with type I DM. The duration of diabetes ranged from 3years to 13 years with a mean of 2 years. Their age ranged from 1-19 years with a mean of 10 years. At the time of enrollment, the patients or their parents filled a questionnaire giving information about age, age at the onset of diabetes, duration of diabetes and personal history of thyroid disorder. Physical examination included signs of thyroid dysfunction and estimation of thyroid size. Thyroid size was classified according to the WHO classification into auto-antibodies in Sudanese children with type 1 diabetes mellitus Sara N Mohamed 1 *, Mohammed O Hussien 1 , Abd Elrahim M El Hussein 1 , Inaam N Mohamed 2 , Mohamed A Abdullah 2 1 Central Laboratory, Ministry of Science and Technology, Khartoum-Sudan. 2 Department of Paediatrics, Faculty of Medicine, University of Khartoum, Khartoum-Sudan Abstract Objective: The association between autoimmune thyroid disease and type I diabetes mellitus is well known. However, racial variation in the prevalence of antibodies is well recognized. The objective of this study was to see the prevalence of autoimmune thyroid disease among Sudanese children with type I diabetes mellitus. Methods: This is a cross sectional study. Sera from 150 Sudanese children (100diabetics and 50 controls) were examined for thyroid peroxidase autoantibodies, after obtaining consent and taking history and examination. TSH and T4 were done on those with positive antibodies. Results: Six children (6%) and none of the control had positive antibodies. One of them had hypothyroidism. The female to male ratio was 2:1. The duration of diabetes on those with positive antibodies varied from onset to 13 years. The mean age of those with positive antibodies was 14.5 years Conclusion: Our findings show the high prevalence of autoimmune thyroid disease among children with type IDM as is the experience elsewhere, and we concur with the recommendation of regular screening of these patients for this problem. * Corresponding author: Central Laboratory, Ministry of Science and Technology, Khartoum-Sudan. P.O Box 11111. Email: saragashy@yahoo.com. Tel: +249 9 12985057 Khartoum Medical Journal (2010) Vol. 03, No. 01, pp. 381 - 384 381 The prevalence of thyroid peroxidase