Abstract : The thyroid hormones are responsible for regulation of basal metabolic rate & have effects on almost all body tissues. It has influence on appetite, absorption of nutrients & gut motility. Hashimoto`s thyroiditis represent different phases of an organ- specific, immune mediated inflammatory disorder & are referred as autoimmune thyroiditis. It is characterized by the production of autoantibodies that alters thyroid function. In the present study investigated that the correlation between clinical features, thyroid function tests, antithyroid antibody profile and cytomorphological observation in Hashimoto`s thyroiditis. The cytomorphology in an aspirate is dependent on the phase of the disease. In this study was carried out in the department of Pathology and biochemistry in the period of January 2021to January 2022, Arunai Medical College Hospital and Research Institute. FNAC was performed in all the patients with palpable/visible thyroid swelling. Among 100 cases showing the cytomorphology of autoimmune thyroiditis were selected and it’s correlated with their clinical features, thyroid function test and antithyroid antibody profile. Out of the 100 patients, 15 patients underwent thyroidectomy and sent for histopathological examination. Their results were studied and correlated with other examination. Out of 100 cases under study, majority of cases (66.6%) were categorized into cytological grade II. 35% of cases presented with subclinical hypothyroidism and 33.3% of cases presented with overt hypothyroidism. 89.3% of cases showed elevated levels of antithyroid peroxidase antibody. Cytomorphological grading of Hashimoto`s thyroiditis can explain the pathogenesis of this autoimmune disease. serology is an useful adjunct for the diagnosis of autoimmune thyroiditis, in cases with negative antibody titers and/or biochemically euthyroid & subclinically hypothyroid cases, FNAC continues to be diagnosis of Hashimoto’s Thyroiditis patients.