We studied ultrasonographic echo levels of the salivary glands of 60 healthy children using histogram peak levels after noticing that echo levels of submandibular glands of young children appear to be lower than those of adults, while parotid gland echo levels remain relatively constant through time. Peak level of thesubmandibular gland (Ls) increased with age (correlation coefficient, 0.69), while peak level of the parotid gland (Lp) was stable. To evaluate normal submandibular echo levels in children, we calculated the difference between the echo levels in the parotid gland and the submandibular gland (Lp-Ls) in order to cancel the variances of subcutaneous tissue for histogram measurement. Lp-Ls values ranged from 15 in infants to 1 in adolescents. Negative correlation was clearly demonstrated between Lp-Ls and age (correlation coefficient, -0.85). We measured Lp-Ls of 15 adults who were used as controls. Mean value in the adults was 2.0±2.3 (SD). A patient with submandibulitis had a much higher Lp-Ls value than would be expected in a person of his age. Histologic study of submandibular glands obtained from twelve autopsy specimen from 3-month-old to 10-year-old children showed increase in fat content of the tissue with age. In this study, submandibular echo level increased with age and reached the adult level around school age. These findings suggest that fat content may contribute to the echo level of the submandibular gland. It is of great importance to know the normal echo levels of normal salivary glands in children.