We present an additional sonographic sign of Hashimoto’s thyroiditis (HLT), increasing the specificity of this method in pediatric populations. Methods: A total of 98 children (mean age 12.7 years, range 7–17 years) were selected from the registry of the endocrinology outpatient department. All subjects met the diagnostic criteria for HLT. All children underwent a prospective thyroid ultrasound examination with special attention paid to the presence of lymph nodes adjacent to the thyroid gland. In order to form a control group, we analyzed 102 healthy volunteers and 94 children with cervical lymphadenopathy, age- and sex-matched with the main study group. Results: The ultrasound of the thyroid revealed typical sonographic signs of autoimmune thyroid disease in all children with HLT and in none of the individuals in the control groups. In 96 children (98%) from the HLT group, at least 2 lymph nodes adjacent to the lower part of the thyroid gland lobes localized on one or both sides of the thyroid were detected. No lymph nodes adjacent to the lower part of the thyroid lobes were found in healthy children or children with cervical lymphadenopathy. Conclusions: Lymph nodes adjacent to the lower part of the thyroid lobes are an additional ultrasound sign of pediatric Hashimoto’s lymphocytic thyroiditis, with 98% sensitivity and 100% specificity.