Most breast disease in adolescents, including that resulting in surgery, is benign; however, malignant conditions do occur. The distribution of diagnoses in adolescent females undergoing breast surgery was determined. Records and histologic material were reviewed from 185 females under 18 years of age. The patients range in age from 11 to 17 years, median 16 years. One hundred patients (54%) had surgery for fibroadenoma. Twenty-four patients (13%) had reduction mammoplasty. Although juvenile or “virginal” hypertrophy is a subjective diagnosis, more than 500 g of breast tissue was excised in 10 patients. The spectra of “fibrocystic” and proliferative breast disease was identified in 44 patients (24%). Four patients (2.6% of those with breast mass) had malignant neoplasms: a 15-year-old with primary rhabdomyosarcoma, a 17-year-old with metastatic rhabdomyosarcoma, a 13-year-old with metastatic neuroblastoma, and a 12-year-old with non-Hodgkin's lymphoma. The remaining diagnoses were 4 polythelia, 2 accessory breast tissue, 2 mastitis, 2 intramammary lymph node, 2 hemangioma, and 1 fat necrosis. Although fibroadenoma is the most common breast mass (65% of masses) in adolescents undergoing breast surgery, a variety of other conditions may necessitate surgery for diagnostic and/or therapeutic purposes. In this study, 2.6% of patients with breast mass had a malignant neoplasm. Therefore, malignancy must be considered in the diagnosis and the consideration for surgery in adolescent females presenting with breast mass.