Study was conducted on 175 cirrhosis patients treated in Bach mai Gastroenterology Department to find out frequency of hyponatremia and risk factor of hyponatremia in cirrhosis. The results showed that hyponatremia was found in 110/175 (63 percent). Hyponatremia (sodium 130 mmol/I) was found 60/175 (34.3 percent). Out of 60 patient with hyponatremia " 130 mmol/l), 51 were in Child-Pugh C class (p 0.05). The cirrhosis related complication were also significantly increased in patients with hyponatremia than in patient with normal serum sodium. In conclusion, Hyponatremia is frequent in cirhosis patient especial patient with server ascites, hepatic encephalopathy, hepatorenal syndrome. Hyponatremia is prognostic factor in cirrhosis.