Juvenile hypertrophy of the breast (JHB) is an uncommon, benign disorder and typically occurs in peri-pubertal females. The etiology of JHB is uncertain. It may represent an end-organ hypersensitivity of the breast to normal levels of sex steroids. Clinically, it is characterized by rapid enlargement of breasts, either unilateral or bilateral. The definitive diagnosis is made by histopathologic examination. Treatment recommendations include surgery and hormonal therapy, although hormonal manipulation is still controversial in pediatric patients. Here we report a 13-year-old girl with unilateral JHB who did not require surgery or medical treatment.