Background <p>Breast masses in adolescents are predominantly benign and are most commonly associated with fibroepithelial tumors. These tumors represent a heterogeneous group of biphasic lesions, ranging from benign fibroadenomatoid changes to malignant phyllodes tumors. Differentiating between fibroadenomas and phyllodes tumors is clinically significant owing to their differing malignant potential and the consequent implications for treatment strategies. However, this distinction is often challenging, as the two entities share considerable overlap in both clinical presentation and imaging characteristics. For this reason, surgical excision of the mass followed by histopathological evaluation remains essential to ensure accurate diagnosis and to prevent overlooking malignant forms with metastatic potential. Giant juvenile fibroadenoma, a rare subtype of fibroadenoma, accounts for approximately 0.5–4% of cases in adolescents. Although histologically benign, its characteristic rapid growth frequently necessitates surgical intervention to alleviate symptoms and exclude malignancy.</p> Case presentation <p>We present the case of a 19‑year‑old female individual of Oromo ethnicity who developed a rapidly enlarging mass in the right breast. Surgical excision was performed, and histopathological evaluation confirmed the diagnosis of giant juvenile fibroadenoma.</p> Clinical discussion <p>Giant juvenile fibroadenoma is an uncommon subtype of fibroadenoma, accounting for approximately 0.5–4% of cases in adolescents. It is defined by a tumor weight exceeding 500&#xa0;g, a diameter greater than 5&#xa0;cm, or a mass occupying more than four-fifths of the breast. Characteristically, it demonstrates rapid growth, leading to distortion and compression of the breast parenchyma. Although benign, its aggressive enlargement is particularly observed in children and adolescents. Diagnosis is primarily based on clinical evaluation and imaging studies. Clinically, the lesion presents as a well‑circumscribed, mobile mass with elastic consistency and clear contours, often resulting in breast deformity and aesthetic discomfort. Ultrasonography serves as the principal diagnostic modality, typically revealing a large, homogeneous, hypoechoic lesion. Given its rapid growth, surgical excision is the treatment of choice. Excision is warranted not only to prevent potential damage to the mammary gland but also to address cosmetic concerns and mitigate the negative impact on the patient’s quality of life.</p> Conclusion <p>Although fibroadenomas, benign fibroepithelial lesions, represent the most common breast tumors in children and adolescents, histopathological confirmation remains indispensable to prevent misdiagnosis and to avoid overlooking malignant variants with metastatic potential.</p>