<h3>Objective:</h3> The objective of this study was to describe the prevalence of anti TPO ab among FM patients, their thyroid status and to evaluate clinical response to corticosteroids. <h3>Background:</h3> Fibromyalgia (FM) is a disorder characterized by widespread musculoskeletal pain and other somatic symptoms. Studies have shown that there is a high prevalence of anti TPO ab (Thyroid peroxidase antibody) positivity among FM patients. It is unknown if thyroid autoimmunity is a predisposing factor for FM. <h3>Design/Methods:</h3> We included 107 patients who were diagnosed with FM based on 2010 American College of Rheumatology Criteria who attended our neurology clinic at Appusami Hospital, India between July 2019 and 2022. We recorded data including age, gender, thyroid profile, anti TPO titer [Negative (<15), positive (15 to 500), strongly positive(>500)] and calculated age adjusted odds ratio for steroid responsiveness. <h3>Results:</h3> Mean age of the study group was 48.29 and 78.5% were females. In our series, 75.7% of FM patients had positive anti TPO ab (Positive- 41.12%;strongly positive-35.51%). 51.40% were euthyroid, 38.32% were hypothyroid and 10.28% were hyperthyroid. Overall 56.8% responded well to steroids. (80.85% of strongly positive;19.15% of positive patients). Age-adjusted odds of steroid response in patients with higher anti TPO ab is 5.2 times that of the one with low ab (p<0.001) (95%CI 3.03;9.04) <h3>Conclusions:</h3> Thyroid autoimmunity is frequently associated with middle aged women with FM. Higher anti TPO ab titers strongly correlated with steroid responsiveness in our study and we recommend a short course of steroids for this subset of patients. These findings need to be confirmed with a larger prospective study. Further research should focus on understanding the pathophysiology of FM and it9s the causal relationship with thyroid autoimmunity. <b>Disclosure:</b> Dr. Eswaradass has nothing to disclose. C Eswaradass, 303 has nothing to disclose. Dr. Thermalingem has nothing to disclose. Dr. Thirunavukkarasu has nothing to disclose. Dr. Gurunathan has nothing to disclose.