The usefulness of sonography in determining the location and internal consistency of a pelvic mass and in predicting a specific diagnosis was assessed in 70 girls ranging in age from neonate to 19 years. Sonography was correct in determining the site of origin in 39 of 40 surgically proven cases. Among the various sonographic patterns observed, cystic uterine masses and cystic adnexal masses were the most specific, representing hydrometrocolpos or intrauterine pregnancy and benign ovarian cysts, respectively. A nonspecific sonographic pattern was encountered with complex or solid adnexal masses, which were proven to be ovarian teratomas, hemorrhagic ovarian cysts, and pelvic abscesses. Occasionally, a specific diagnosis of ovarian teratoma could be made when echogenic foci produced shadowing in a complex adnexal mass. Our results indicate that sonography in girls is reliable in determining the site of origin of a mass and can suggest a specific diagnosis of hydrometrocolpos, benign ovarian cyst, or intrauterine pregnancy.