Objective:To analyze the correlation between serum claudin-1(Cla-1) level and the risk of papillary thyroid carcinoma(PTC) in patients with thyroid nodules.Methods:The clinical data of 345 patients with thyroid nodules were retrospectively analyzed. According to the pathological results, they were divided into PTC group and benign thyroid nodule(BTN) group. The difference of serum Cla-1 level between 2 groups and its correlation with the risk of PTC were analyzed.Results:In groups of PTC( n=225) and BTN( n=120), the median value of serum Cla-1 level was 14.03(10.30, 20.40) ng/mL. The differences in the median value[17.90(14.00, 22.93)ng/mL vs 9.40(8.15, 11.20) ng/mL] of serum Cla-1 level in the PTC and BTN were statistically significant by Wilcoxon signed-rank test. The prevalence of PTC in thyroid nodules increased gradually with increasing of serum Cla-1 level. Receiver operated characteristic curve analysis showed that the best diagnostic cut-off value of the PTC was 13.02 ng/ml of which the sensitivity was 81.8%, the specificity was 89.2%, and the area under curve(AUC) was the largest(AUC=0.944, P<0.01, 95% CI 0.922-0.965). Logistic regression analysis showed that elevated serum Cla-1 level increased the risk of PTC, and it was statistically significant( OR=4.334, 95% CI 1.662-11.303, P=0.003). There was a significant correlation among the serum Cla-1 level and gender, age, location of involvement, number and diameter of cancer nodules, extracapsular invasion of thyroid, lymph node metastasis, tumor stage and combined with Hashimoto′s thyroiditis( P<0.01). Conclusion:The serum level of Cla-1 may be one of risk factors to predict PTC, and it is related to the total amount of PTC tumor cells in vivo, but it was not related to the aggressive behavior of tumor.