This study was performed to establish the reference for tonsil size in children, including neonates, without tonsil-associated symptoms, in relation to anthropometric indices (sex/age/height/weight/body mass index).We evaluated the size of both tonsils in 362 children by ultrasonography. Tonsil size was calculated as 0.523abc (a, transverse diameter on the transverse image; b, longitudinal diameter on the transverse image; c, longitudinal diameter on the longitudinal image) and compared between each age year using the Wilcoxon signed rank sum test with Bonferroni correction. We evaluated the relationships between tonsil size and anthropometric indices.Among these children, tonsil size was significantly increased by the age of 3 years (0-1 vs 1-2 [volume (right) = 210.15 ± 205.27 vs 737.83 ± 335.72 mm, P (right) < 0.0001 and volume (left) = 218.26 ± 207.23 vs 645.33 ± 240.31 mm, P (left) < 0.0001]; 1-2 vs 2-3 [volume (right) = 737.83 ± 335.72 vs 1073.86 ± 468.21 mm, P (right) = 0.004 and volume (left) = 645.33 ± 240.31 vs 1109.73 ± 563.20 mm, P (left) < 0.0001]). Although there was a tendency for the tonsil size to increase in years 3-12, there was no significant difference. Using single linear regression analysis, we found a correlation between tonsil size and age (r right/left = 0.67/0.65), height (r right/left = 0.72/0.70), and weight (r right/left = 0.66/0.64), with height having the strongest correlation.In conclusion, tonsil size significantly increased by 3 years of age. Tonsil size was correlated with anthropometric indices, with height showing the strongest correlation.