Phyllodes tumor (PT) is a tumor similar to fibr o adenoma, that can reach to enormous sizes. It consistic less than 1 % of all breast neoplasms. Here, a 13 years old female patient is reported due to its rarity. She presented with a mass in the right breast which showed hard consistency and fixation to the thoracic wall by palpation and caused retraction of the nipple. Tomography revealed a solid mass with the diameter of approximately 11 cm. Patient was operated with the presumptive diagnosis ofPT or breast carcinoma and the mass was totally excised together with its capsule. Pathologic examination showed 6 mitotic cells in each field, medium cellularity and slight atypia. It was accepted as a borderline tumor but no recurrence or metastasis was observed within postoperative 5 months. As for conclusion, PT should be considered in rapidly expanding masses of breast that present with enormous size.