Hashimoto's Thyroiditis is prevalent among type 1 diabetic patients. Prevalence rate can be dependent on many factors like geographical area, level of HbA1C, duration of diabetes, age & BMI of the patient. This study aimed to investigate the prevalence of Hashimoto's Thyroiditis among insulin dependent diabetes mellitus patients in the Jaipur district. This prospective, single-centered & clinical-based study includes a total of a hundred and twenty-five subjects (87 males & 38 females) with type 1 diabetes among them 10.4% were children, 41.6% were Adolescents, and 48% were Adults. The age ranged from 4 to 65 years (mean age 21.42 ± 11.02) selected from Endocrine OPD of Sawai Man Singh (S.M.S) Medical College and Hospital, jaipur, rajasthan between June 2017 and August 2017. Mean age, extent of diabetes, and BMI of subjects were determined according to the physical examination and information collected through Performa. Detailed clinical examination was done to detect Hashimoto's thyroiditis followed by appropriate hematological and biochemical investigations like Fasting Blood Sugar (FBS), Glycosylated Hemoglobin (HbA1c), Thyroid Stimulating Hormone (TSH), and Anti-Thyroid Peroxidase Autoantibodies (Anti-TPO). Categorical data were analyzed by Chi-Square test & continuous data was analyzed by Pearson Correlational test & p-value was calculated. After screening, 44% of patients had sera-positivity for Anti-TPO (55 out of 125) & 56% (70/125) of patients had negative for Anti-TPO. Among fifty-five autoimmune thyroiditis patients, 12 (0% Children, 16.7% Adolescents, & 83.3% Adults) were women & 43 (7% Children, 32.5% Adolescents, & 60.5% Adults) were men. Patients with higher anti-TPO titer were comparatively older than those who had anti-TPO levels within the normal range (mean age of the subjects respectively 24.4 ± 11.61, 19.07 ± 10.13). Patients with positive anti-TPO had a higher BMI (21.26 ± 9.69) than patients who were negative (17.9 ± 2.79) for autoimmune thyroiditis. It is also observed that the duration of diabetes has a positive correlation with the level of anti-TPO, r value – 0.3204. In conclusion, Thyroiditis is more prevalent in adults than children & adolescents with type 1 diabetes. Regular screening of thyroid antibodies may be suggested in all type 1 diabetic patients. [ABSTRACT FROM AUTHOR]