Abstract： Objective To explore the value of serum thyroid hormones in assessing the severity of acute pancreatitis early in its course.Methods Fifty-two patients with acute pancreatitis were included in this prospective study.Attacks were classified as severe ( n =32) or mild ( n =20) according to the Atlanta criteria.Serum levels of thyroid hormones,including FT4,FT3,rT3 and TSH,were measured at admission.Each of the thyroid hormone levels was compared between the severe and mild groups,and the relationships of these thyroid hormones with APACHE Ⅱ scores and CT severity grading were analyzed.Effectiveness of thyroid hormone for the prediction of disease severity was evaluated by receiver operating characteristic (ROC) curve analysis.Results Serum FT3 levels were decreased significantly in severe acute pancreatitis compared with those in mild acute pancreatitis (P ＜ 0.01 ) ; whereas no significant difference was noted in the levels of FT4,rT3 and TSH between groups (P ＞ 0.05 ).Serum FT3 levels were negatively correlated with APACHE Ⅱ scores ( r =- 0.687,P ＜ 0.01 ) and CT severity grading ( r =- 0.720,P ＜ 0.01 ).The area under curve of FT3 was 0.875.With an optimum cutoff value of 2.87 pmol/L for FT3,the sensitivity,specificity,positive predictive and negative predictive values for the prediction of severe acute pancreatitis were 75％,95％,93.8％,and 79.2％,respectively.Conclusions Serum FT3 level is an acceptable indicator for early assessment of the severity of acute pancreatitis.