['Although ultrasound (US) features of papillary thyroid carcinoma (PTC) are well established, little is known regarding biological behavior according US features. We investigated whether there was a difference in biological behavior between PTCs that did and did not meet malignant US criteria.', "We retrospectively reviewed clinical records and histological and US findings of the index tumors in 488 patients who underwent surgery for PTC. Benign-looking PTC (B-PTC) was defined as showing none of the accepted US criteria for malignancy. Malignant-looking PTCs (M-PTCs) and B-PTCs were compared in terms of patients' age, sex, tumor size, histological subtype, multifocality, lymph node (LN) metastasis, extrathyroidal extension, stage, recurrence, and distant metastasis.", 'B-PTCs accounted for 74 (15%) of all 488 PTCs. Mean tumor size was not significantly different between the groups, with 1.10 cm for M-PTC and 1.11 cm for B-PTC (P = .947). Univariate and multivariate analysis indicated that M-PTC more frequently had LN metastasis, extrathyroidal extension, and a higher stage than B-PTC (all P < .05). The results were significant in tumors ≥1.0 cm, whereas there were no significant differences in tumors <1 cm. As the number of malignant US features increased, multifocality, extrathyroidal extension, LN metastasis, and a higher stage were more likely.'] Do preoperative ultrasonographic features of papillary thyroid carcinoma predict biological behavior?