Abstract Background The purpose of this study was to assess the diagnostic performance of preoperative ultrasonography (US) for the prediction of extrathyroidal extension (ETE) in patients with papillary thyroid carcinoma (PTC) and to compare the diagnostic performances of US and magnetic resonance imaging (MRI) for predicting ETE. Methods 75 patients with PTC who underwent preoperative US and MRI were retrospectively reviewed in this study. Two radiologists independently evaluated the US and MR findings to assess minimal or extensive ETE of PTC. These results were compared with the histopathologic findings. The diagnostic performances of US and MRI in the evaluation of ETE were compared. Results US was more accurate than MRI in the prediction of minimal ETE (p < 0.05) and the accuracies were not significantly different between US and MRI in extensive ETE. US showed higher sensitivity, negative predictive value and accuracy than MRI (p < 0.001) in the prediction of overall ETE. Conclusion US provided higher accuracy for assessing overall ETE and higher sensitivity for minimal ETE than MR imaging in preoperative evaluation of ETE of PTC. There was no significant difference in evaluating extensive ETE of PTC between US and MRI.