The present case report is about a 52-year-old hypothyroid female who was brought by family members with history of recurrent episodes of seizures in last ten days with progressively increasing altered behavior for same duration. There is history of recent, remote memory loss associated inability to carry out activities of daily living. Amongst medical co-morbidities she is hypothyroid (on regular thyroxin replacement 75 mcg/day). Upon neurological examination GCS was 10, no meningeal signs, no cranial nerve palsy, power 3/5 in all four limbs with normal tone. Pupils are bilaterally symmetrical and normally reacting to light, plantar bilateral flexor, deep tendon reflexes are normal. No sensory loss, no meningeal or cerebellar signs, no cranial nerve palsies. Fundus was normal. At admission, complete hemogram, fasting blood sugar, electrolytes, kidney function tests and liver function tests were normal. CSF study at admission had 62 cells with all lymphocytes, protein of 151 mg/dl with sugar of 76 mg/dl. HIV, HBsAg, Anti-HCV-nonreactive. ANA (Hep2 method)-negative, ANA profile-negative. CSF and serum VDRL were negative. Thyroid profile revealed euthyroid state. Anti-Thyroid peroxidase (TPO) Antibody-431.8; (normal<35). Anti-TG antibody-negative. Anti-NAE autoantibodies were positive. VGKC Ab, NMDA receptor Ab A 52-year-old hypothyroid presented with episodes of seizures in last ten days with altered behavior. CT scan of brain showed cerebral atrophy and MRI of brain revealed non-specific changes. In EEG, there was slow wave pattern. CSF study showed increased cell count with all lymphocytes and raised protein with normal glucose. Anti-TPO Antibody was positive. All relevant investigations like HIV, HBsAg, Anti-HCV Ab, ANA (Hep2 method), ANA profile, P-ANCA, c-ANCA, VGKC (voltage gated potassium channel) Ab, NMDA Receptor/Anti-Glutamate Antibody) Ab, VDRL were negative. She was given pulse doses of methylprednisolone followed by maintenance prednisolone. Then her GCS improved followed by sudden deterioration. Repeat CSF showed marginal decrement of protein and cell count. Then she was given IV Immunoglobulin and patient improved. At discharge her CSF study normalized. Anti-TPO Ab titre came to normal level and EEG normalized. Hashimoto's encephalopathy(HE) should be suspected in a case of sub-acute encephalopathy with high levels of anti-thyroid antibodies may be with normal thyroid functions. Here the patient did not have improvement on steroids. The patient needed immunoglobulin to improve.