OBJECTIVE: To establish ultrasound reference values for thyroid volumes in children up to 3 years of age, given that ultrasound of the thyroid is an essential examination in the diagnosis of childhood thyroid disease. MATERIALS AND METHODS: This was a prospective study conducted in an iodine-sufficient city in southeastern Brazil. A total of 100 healthy children underwent clinical evaluation, anthropometric examination, and cervical ultrasound in accordance with conventional protocols. We evaluated characteristics such as echotexture, thyroid lobe volume, and total thyroid volume. The children were divided into five groups, by age: < 2 months; 2–12 months; 12–18 months; 18–24 months; and 24–36 months. RESULTS: The mean thyroid volume was lower in the < 2 month age group than in the other groups (0.4 mL vs. 0.18–0.70 mL; p < 0.001). For the subjects between 2 and 36 months of age, the mean volume was 1.0 mL (range, 0.30–2.0 mL). No other significant differences were observed between groups, thyroid lobes, or gender. However, body mass index correlated significantly with total thyroid volume (r = 0.347; p = 0.001). CONCLUSION: The mean thyroid dimensions were smallest in the < 2 month age group (0.35 ± 0.16 mL). For the subjects between 2 and 36 months of age, a reference value of 0.85 ± 0.42 mL can be used. Our data could guide the diagnostic investigation of thyroid disease, especially congenital hypothyroidism, in childhood.

Keywords: Thyroid diseases; Congenital hypothyroidism; Ultrasonography; Child development; Child health.