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Objectives: Olfactory dysfunction is an overlooked adverse effect of radiation therapy. This study is designed to find the effect of radiation therapy on olfactory function in head and neck malignancy excluding tumors of nose and nasopharynx and correlate the olfactory changes with the radiotherapy dose., Method: This prospective observational study was done over a 2-year period in 34 participants with head and neck malignancies who underwent radiation therapy (RT). The participants olfaction was evaluated subjectively with Italian Nose Obstruction Symptom Evaluation (I-NOSE) scale and objectively by a modified I-Smell test which included an olfactory identification score and an olfactory threshold score at 5 time points. The beginning of RT ( T 0), at 2 weeks of RT( T 1), end of RT ( T 2), 1 month follow-up ( T 3), and 3-month follow-up ( T 4). The near maximum dose to the nasal cavity ( D 2% ) and mean dose to the nasal cavity ( D mean ) were calculated for all participants and correlated with olfactory function., Results: A total of 34 patients with head neck malignancy were recruited. The median I-NOSE score reached maximum at the end of radiation and decreased to baseline at 3 months follow-up ( P  < .001). The olfactory identification score, olfactory threshold score, and median combined olfactory score showed a significant decrease at the end of radiation therapy compared to Pre-radiation therapy values. There was a significant but incomplete recovery in the 3-month follow-up period ( P  < .001)., Conclusion: There was a significant deterioration in quality of life for olfaction, olfactory identification, and olfactory threshold at the completion of radiotherapy. At 3 months follow-up, though there was no complete recovery of olfaction, it did not have an adverse effect on the quality of life., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.