Sonography was performed in 17 pediatric patients with 18 benign cystic teratomas of the ovary in order to compare the appearance of this entity in prepubertal and postpubertal girls. Particular attention was paid to the frequency of the characteristic features of the lesion, particularly mural nodules and acoustic shadowing. Of the eight lesions in children less than 13 years old, five were complex lesions and three were cystic. Mural nodules were found in three (38%) of eight lesions and acoustic shadowing in one (13%). Of the 10 lesions in the patients 13 years old or more, seven were complex and three were solid. Seven (70%) of 10 lesions contained a mural nodule, seven (70%) had acoustic shadowing, and one (10%) had a fluid/fluid level. Our experience suggests that typical sonographic features of ovarian teratomas occur more frequently in postpubertal than prepubertal girls.