BACKGROUND Hyponatraemia is one of the commonest electrolyte abnormalities among admitted patients. It is also the commonest electrolyte abnormality associated with morbidity and mortality. Hence, we aimed to study the clinical and aetiological profile of patients admitted with severe hyponatraemia in Pondicherry Institute of Medical Sciences, Pondicherry. MATERIALS AND METHODS A prospective observational study conducted at tertiary care hospital in South India during last 18 months. All patients above age of 18 presenting with serum sodium less than or equal to 125 mEq/L were included in the study. Detailed medical and surgical history was recorded. Routine investigation like complete haemogram, renal function test, serum electrolytes, thyroid function test, serum cortisol and urine spot sodium and osmolality were done. Descriptive variables were expressed in mean and standard deviations. They were compared using Mann-Whitney U test and x 2 test.