【Abstract】 Objective：To assess the ultrasonographic features affect false negative,falsepositiveofextrathyroid extension(ETE) evaluation on preoperative ultrasonography in papillary thyroid microcarcinoma(PTMC) .Methods:Between January 2016andJanuary 2019,326consecutive patients (472nodules) underwent surgery for pathologically confirmed PTMCs. We analyzed the medical records of all patients with PTC with preoperative USscan to calculate the sensitivity, specificity, positive predictive value (PPV), negative predictive value（NPV)and accuracy of the presence of ETE. The diagnostic performances of US in the evaluation of ETE using the χ2 test.The factors associated with false-negative(FN) and false-positive(FP) results for ETE were analyzed.Results: The sensitivity, specificity, PPV, NPV, and accuracy for predicting ETE according to sonographic criteria were 51.7%,86.7%,62.4%,80.8%和73.6%, respectively.In univariate analysis showed that diameter of tumor ≤5mm, taller than wider shape, vicinity to the trachea (non-adjacent) and non-bilaterality were associated with FN（P＜0.05）;multiple logistic regression analysis showed that vicinity to the trachea (non-adjacent) ,non-bilaterality is independent risk factor for FN（OR＝4.916、7.237，P＜0.05）.In univariate analysis showed that diameter of tumor ≤5mm is associated with FP（P＜0.05）.