Objective To investigate the factors associated with hyponatremia after pituitary adenoma surgery and its prognosis.Methods Clinical data of 120 pituitary adenoma patients treated in our hospital form Jan.2008 to Dec.2010 were retrospectively collected.The incidence of hyponatremia after surgery,clinicopathology and related treatment were analyzed.Results In the 120 patients,28 (23.3％) occurred hyponatremia.The blood natrium concentration recovered to normal in 7 patients within 3 days,and in 21 patients within 4 -7 days.Hyponatremia was associated with age,size of adenoma,type and diabetes insipidus early after surgery(x2 =12.6,12.4,5.38 and 6.51,Ps ＜0.05).Conclusion Hyponatremia after pituitary adenoma surgery is frequent in patients with giant pituitary adenoma,history of diabetes insipidus and older than 50 yrs.Monitoring blood electrolyte and treatment with sodium in 1 - 2 weeks after surgery would be helpful to prevent potential severe compilations.