Objective. To assess the sonographic findings of breast masses in adolescents and the usefulness of sonographic patterns for suggesting a specific diagnosis. Methods. The sonograms and medical records of 57 girls (mean age, 15.4 years) with palpable breast masses were retrospectively reviewed. Three observers reviewed the sonograms for multiple sonographic findings. Surgery or clinical findings established diagnoses. Statistical analysis was done to determine how well sonographic findings alone and in combination agreed with final histologic diagnoses. Results. Diagnoses included cysts (n = 12), abscesses (n = 7), fibroadenomas (n = 36), a lactating adenoma (n = 1), and a phyllodes tumor (n = 1). The sonographic findings varied significantly among lesion types (P ≤ .005). Conclusions. Our experience suggests that virtually all breast masses in a pediatric population are benign and that sonography has the ability to differentiate among cystic, inflammatory, and solid masses. Key words: sonography; breast; mass; adolescent. onography has become a widely used modality for characterizing breast masses in adults as cystic or solid, and it has been shown to be highly reliable for this purpose. [1][2][3][4][5] Although the specificity of various sonographic patterns has been reported in breast masses in adults, similar data are lacking in pediatric patients. Previous series have included small numbers of children 6 or were primarily performed with older technology. 7 In view of the advances in technology and the development of high-frequency transducers, a reevaluation of the role of sonography in the clinical evaluation of the pediatric breast is appropriate. We thus undertook this study to determine whether there are gray scale sonographic findings that are helpful in differentiating breast masses in adolescents.