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). Condusions. 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.