AbstractPolycystic ovarian syndrome (PCOS), the commonest endocrinological abnormality of women in the reproductive age, is adversely affected by associated thyroid dysfunction. Both have independent risks for ovarian failure and complications related to pregnancy. Aim of the study: The present study aims to investigate the prevalence of different thyroid disorders in PCOS patients. Settings and Design: Observational case control study. Materials and methods: This hospital based observational case-control study was done in 90 cases who were defined as having PCOS according to the revised 2003 Rotterdam criteria and another 90 age-matched women were studied as the control population. Thyroid function was evaluated by measuring serum thyroid stimulating hormone (TSH), free T3 and free T4 levels, anti-thyroperoxidase antibody (anti-TPO Ab) and thyroid morphology by clinical examination and ultrasound (USG) of the thyroid gland. Statistical Analysis: It was done by Student’s t-test and Chi-square test using appropriate software (SPSS version 25). Results: This case-control study revealed statistically significant higher prevalence of autoimmune thyroiditis, detected in 17 patients (18.9% vs. 1% of control) as evidenced by raised antiTPO antibody levels. PCOS patients were found to have higher mean TSH level than that of the control population (4.52 ± 2.56 and 2.54 ± 3.15 respectively; p value < 0.05). Also a high prevalence of goiter was observed among PCOS patients (27.8% vs. 8.9% of control, p value < 0.001). On thyroid USG, 16.67%of PCOS patients and 4.44% of controls had hypoechoic USG pattern which was also compatible with the diagnosis of autoimmune thyroiditis. Conclusions: High prevalence of thyroid disorders in PCOS patients necessitates the importance of early screening and correction of hypothyroidism in managing infertility associated with PCOS.