Background Although metastasis of lateral cervical lymph nodes (LNs) is common in papillary thyroid carcinoma (PTC), correctly diagnosing small metastatic LNs with US remains challenging. The use of contrast-enhanced US (CEUS), especially the postvascular phase of CEUS with perfluorobutane contrast material, might contribute to improved diagnosis of metastatic LNs in PTC. Purpose To assess the diagnostic value of the postvascular phase of CEUS with perfluorobutane in suspicious small lateral cervical LNs (short-axis diameter ≤8 mm) in patients with PTC. Materials and Methods This single-center study prospectively enrolled consecutive participants with confirmed PTC and suspicious LNs at US from October 2020 to October 2021. All participants underwent CEUS, 1 week before biopsy or surgery, with intravenous perfluorobutane contrast material to visualize the LNs in the vascular phase (5-60 seconds after injection) and postvascular phase (10-30 minutes after injection). The reference standard was cytologic and surgical histologic assessment of the LNs. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of sonographic features were calculated, and the diagnostic performance of US, CEUS, and the combination of postvascular phase and US features was assessed using multivariable logistic regression models. Results A total of 135 participants (median age, 36 years [IQR, 30-46 years]; 100 women) with 161 suspicious LNs at US were evaluated, including 67 metastatic and 94 benign LNs. The specificity of perfusion defect as a sonographic feature in the vascular phase reached 96% (90 of 94 LNs), and the negative predictive value of non-isoenhancement (ie, hypoenhancement, partial enhancement, and no enhancement) in the postvascular phase reached 100% (83 of 83 LNs). The area under the receiver operating characteristic curve (AUC) of the combination of postvascular phase and US features was 0.94 (95% CI: 0.89, 0.97), significantly higher than that of US features alone (AUC, 0.73; 95% CI: 0.65, 0.79; P < .001). Conclusion The postvascular phase of CEUS with perfluorobutane demonstrated excellent performance for diagnosing suspicious small lateral cervical LNs in participants with PTC. Published under a CC BY 4.0 license Supplemental material is available for this article. See also the editorial by Gunabushanam in this issue.