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Abstract : Aim An increased incidence of hyponatremia was noticed among patients with head and neck malignancies on external beam radiation therapy. Hence, we have retrospectively assessed the incidence and patterns of hyponatremia and also the factors that might influence hyponatremia, in patients with head and neck malignancies, as an institutional audit. Materials and Methods Patients with head and neck cancers treated with radical intent from January 2011 to December 2012 were analysed. Data from electronic medical records were retrieved. Patients were grouped, based on their sodium status while on treatment, into group I (hyponatremic) and group II (eunatremic). Each of these groups were sub-grouped as A and B based on treatment interruptions. Univariate and multivariate analysis of individual variables were done.Results Study group included 271 patients. 68.3% of patients had developed hyponatremia. Age greater than 50 years was a significant factor in the development of hyponatremia in multivariate analysis (p- 0.018). Advanced stage was associated with a greater proportion of patients developing hyponatremia (p-0.001). Surgery prior to radiation (univariate - p-0.009; multivariate - p-0.005) and concurrent chemotherapy (univariate - p-0.001; multivariate - p-0.001) significantly increased the risk of developing hyponatremia. Hyponatremia prior to initiating radiation also carried significant risk of developing hyponatremia on radiation (univariate - p-0.001; multivariate - p-0.001). Incidence of interruptions to radiation treatment was higher in patients having hyponatremia(p-0.002). Conclusion Hyponatremia was significantly associated with age, stage of disease, post-operative status, chemoradiation and with initial hyponatremia albeit correction prior to radiation