A 15-year-old female patient presented to our clinic with rapidly-growing breasts, causing her back and neck pain, mastalgia, and unwanted attention at school. Clinical evaluation showed bilateral enlarged breasts with multiple palpable tumors. Her height and body weight were 1.76 m and 54 kg, respectively. Both ultrasound and magnetic resonance imaging (MRI) were conducted. Histological biopsies showed pseudoangiomatous stroma hyperplasia (PASH). Bilateral diffuse multiple tumors leading to massive bilateral breast enlargement are rare, especially in pediatric patients. To the best of our knowledge, all previous reported cases were patients of 29 years old or older. We present the evaluation and treatment in a rare case of multiple PASH causing bilateral gigantomastia in an adolescent patient. Level of evidence: Level V, therapeutic study.