Aim: Treatment of head-and-neck cancer patients with surgery, radiotherapy (RT), and chemotherapy has been associated with post radiotherapy hypothyroidism (HT). This study was aimed to assess the effect of radiotherapy on thyroid function with head and neck cancer Material and method: We reviewed the prospectively collected thyroid function data of patients treated with concurrent chemo radiotherapy therapy in head and neck cancers. The incidence of post treatment hypothyroidism was estimated. The patient factor, tumor site, and treatment factors possibly associated with HT were evaluated. Results: Of 295 patients, 250 were evaluated for radiotherapy induced hypothyroidism. In this study, 37(14.7%) patients out of 250 developed hypothyroidism at median 6 months of follow up. Univariate and multivariate analyses of age and tumor site identified as a clinically relevant risk. Conclusion: In our study we have recognized hypothyroidism after 3 to 6 months following radiotherapy. Recognizing hypothyroidism (overt or subclinical) early and treating it has benefits. Hence, Thyroid function tests should be made routine and must be started from as early as 3 months.