INTRODUCTION Autoimmune thyroiditis (AIT) is a common cause of goiter in children, and sonographic changes have been reported in more than one-third at presentation. The aim of this study was to evaluate the ultrasound (US) characteristics of the thyroid and the prevalence of thyroid nodules in children and adolescents presenting with goiter in the presence or absence of AIT. METHODS A retrospective review was conducted of the US characteristics of 154 children and adolescents aged <18 years of age with goiter from July 2008 to December 2010. US characteristics were analyzed according to each patient's age, sex, thyrotropin (TSH) levels, and thyroid peroxidase antibody titer (TPOAb). Heterogeneity and nodule prevalence were compared between antibody-positive and -negative goiter. RESULTS Heterogeneity was more common in TPOAb-positive (59/71, 83%) compared to TPOAb-negative goiter (24/46, 52%; p<0.001), but there was no correlation between the presence of heterogeneity and TPOAb titer within the antibody-positive group. Nodules were equally prevalent in children with (17%) and without (17.4%) TPOAb, and there was no correlation between the serum TSH level or TPOAb titer and the presence of nodules. Papillary thyroid cancer (PTC) was diagnosed in 3/71 with positive TPOAb compared to 1/46 with negative antibodies. Pseudonodules were identified in 11/71 antibody-positive and none of the antibody-negative patients. However, during follow-up, two of these were later identified as nodules and one was PTC. CONCLUSION The majority of children and adolescents with goiter had positive TPOAb (71/117). Sonographic heterogeneity was more common among TPOAb-positive patients. However, thyroid nodules and PTC were equally common in both groups. Only 15% of the nodules and none of the PTC were palpable. These data support the utility of thyroid US to detect unsuspected thyroid nodules and PTC in children with goiter. Prospective follow-up studies of children with goiter are needed to formulate recommendations for evaluation with US and fine-needle aspiration.