Thyroid nodules are increasingly recognized in children and are associated with a greater risk for thyroid cancer compared with adults. Thyroid ultrasound is the favored tool for evaluation of thyroid nodules; however, there are limited data regarding the accuracy of thyroid ultrasound to confirm features associated with a low risk of thyroid cancer in children. We examined whether thyroid ultrasound is capable of accurately identifying thyroid nodules at a low risk of malignancy in children. Using a retrospective cohort study design, we identified children age ≤18 years with thyroid nodules and adequate follow-up. Ultrasound images were reviewed independently by two blinded expert radiologists, and ultrasound characteristics were analyzed to determine optimal predictive value and reliability. A total of 417 subjects were found to have thyroid nodules, and 152 subjects had adequate follow-up; 59 (38.8%) of these were diagnosed with thyroid cancer. We evaluated 236 individual nodules. Features most consistent with benign nodules included small size, isoechoic echogenicity, partially cystic structure, sharp or noninfiltrative margins, absent Doppler flow, and absent calcifications. Significant variability was found between expert interpretations of ultrasound features. Thyroid nodule composition appears to be the most sensitive and reliable feature for stratifying the risk of thyroid cancer. Ultrasound accurately identified benign thyroid nodules in 80.9% of subjects (95% confidence interval, 74-86.6). Ultrasonography is useful for the evaluation of thyroid nodules, but we found no combination of ultrasound features sufficient to exclude thyroid cancer without a biopsy.