Hyponatraemia is a very common electrolyte abnormality seen especially in hospitalized patients. It is associated with increased mortality, morbidity and increased length of hospital stay if not addressed properly. Hyponatremia is defined as serum concentration of sodium as less than 135mmol/L. Hyponatremia results from relative excess of total body water to sodium content. Serum sodium concentration is determined by serum water content. Serum concentration of water increases by water intake (driven by thirst or by habit), and it is reduced due to insensible losses from the body like sweating and by urine dilution. The underlying pathophysiological mechanisms leading to hyponatremia depend upon underlying pathological cause leading to disturbances in serum ADH level and urinary water excretion. Hyponatremia can be further divided between mild (Na=130-135 mmol/L). moderate (Na=125-129 mmol/L) and severe (Na 48 hours) called Chronic Hyponatremia with no symptoms to minimal symptoms. Acute Hyponatremia (sever) can present with severe CNS symptoms, increased morbidity and mortality and increased ICU admissions. The treatment with hypertonic saline (1.8% and 2.7% NaCl) for severe symptomatic hyponatremia needs careful monitoring in ICU/HDU. Tolvaptan may be considered in patients with high ADH activity, regardless of whether they are euvolemic or hypervolemic. In summary, hyponatremia should be managed according to the underlying etiology, the duration and degree of hyponatremia, symptoms severity and patients' volume status.