Objective To investigate the clinical classification and treatment of hyponatremia after the microsurgery for the lesions in the sellar regions.Methods Twenty-six patients with hyponatremia after the microsurgery for the lesions in the sellar regions were divided into both the hypovolemia group(15 cases) and hypervolemia group(11 cases) according to blood volume.The patients in the hypovolemia group were treated by the supplement of water and sodium,of which,quantity was calculated according to the formula as follows: quantity of supplemented sodium =(normal value of serum sodium-value of measured serum sodium) × body weight×0.2.The patients in the hypervolemia group were treated by restriction of water and diuresis.Results The hyponatremia was improved from 3 days to 2 weeks after the treatment and there were not the severe complications related to the hyponatremia in 23 patients.Two patients died of other complications irrelative to the hyponatremia.One patients gave up the treatment.Conclusions It is simple and practicable that the hyponatremia is classified into the hypovolemia one and hypervolemia one.The patients with hypovolemia hyponatremia should be treated by the supplement of water and sodium,of which,the quantity may be calculated by the above-mentioned formula,and ones with hypervolemia hyponatremia should be treated by the restriction of sodium and diuresis.