Background Serum sodium predicts prognosis in chronic severe hepatitis B and may improve the prognostic accuracy of the model for end-stage liver disease (MELD) score, but the available information is limited. The present study was undertaken to study the clinical use of the serum sodium incorporated MELD (MELD-Na) and assess its validity by the concordance (c)-statistics in predicting the prognosis of the patient with chronic severe hepatitis B. Methods A total of 426 adult patients with a diagnosis of chronic severe hepatitis B between January 1, 2007, and December 31, 2007 at a single center were studied. The scores of serum sodium, MELD, MELD-Na, and △MELD-Na (△MELD-Na=MELD-Na at 14 days after medical treatment -MELD-Na score on admission) of the patients with chronic severe hepatitis B were calculated. The 3-month mortality in the patients was measured, and the validity of the models was determined by means of the concordance (c) statistics.Results The average MELD, MELD-Na scores of survival group were 25.70±5.08 and 26.60±6.90.and those of dead group were 35.60±6.78 and 42.80±9.57 on admission.There was a significant difference in MELD and MELD-Na between the survivaI and dead groups(P