Adolescent patients with breast lesions represent a unique population of patients whose differential diagnoses differ from adults. We report a clinically unsuspected case of alveolar soft part sarcoma (ASPS) presenting in the breast of a 13-year-old female. ASPS is a rare neoplasm that is usually present in the head, neck, or lower extremities. This rare case presentation gives us the opportunity to review the differential diagnosis of adolescent breast lesions. We also will review diagnostic features of ASPS on fine-needle aspiration. These are relatively rare disease processes about which many cytopathology professionals may be unfamiliar. Diagn. Cytopathol. 2009. © 2008 Wiley-Liss, Inc.