Sub acute thyroiditis is a rare disorder of thyroid gland due to viral infection or post viral inflammatory process. It is commonly associated with pain that radiate to different locations in the thyroid gland with tenderness over the neck. A case of sub acute thyroiditis was diagnosed in 40year old male patient who presented with c/o fever since 3 weeks, pain in front of neck radiating to jaw and ear .He had no comorbidities, serological reports were negative for widal, malaria, hepatitis and leptospirosis. On admission he was febrile. On general examination he was conscious and oriented with increased redness and mild tenderness over thyroid region. Ultrasound revealed normal echo pattern of the entire organ. Thyroid function test showed elevated T3 (295 MIU/ML),T4 (21.75 MIU/ML), and low TSH (0.001 MIU/ML) but thyroid antibody test was negative. Liver enzymes were elevated. SGOT(45 IU/L)and SGPT (77 IU/L). Thyroid SCINTI imaging revealed GRADE II Thyromegaly with significantly reduced follicular concentration in both lobes of thyroid with increased vascularity .He was treated pharmacologically with antibiotics ,antipyretics, analgesics, steroid, propranolol and ursodeoxycholicacid.