Background: Very few studies have assessed prevalence of anti-thyroid peroxidase antibodies in women with breast cancer. In this study, we aimed to assess the prevalence of anti-thyroid peroxidase antibodies in women with breast cancer. Methods: Tertiary hospital based cross - sectional study carried out at Saveetha Medical College, Chennai, during the period of August 2018 to July 2020. Seventy-five women in surgical oncology ward/OPD were included in the study. Subjects included in the study were between age 35 to 80 years, provided they fulfilled inclusion and exclusion criteria. History was noted, serum anti-thyroid peroxidase antibodies test was done. Results were noted and analyzed. Results: Out of 75 subjects, 21.3% of women with breast cancer were having elevated antithyroid peroxidase antibodies. Conclusions: Prevalence of anti-thyroid peroxidase antibodies is high among women with breast cancer. These results have implications both for screening of patients for thyroid disorders and also for development of new prognostic markers. Therefore, routine screening is preferable among women with breast cancer.