Pseudosarcomatous myofibroblastic proliferations are very unusual entities of unknown etiology. Despite its benign nature, this entity can easily be misdiagnosed (both clinically and histologically) as a malignant neoplasm. Hereby, we report a case of a 15-year-old woman who presented to our hospital with a broad-based polypoid mass located in the left posterior wall of the urinary bladder. The patient underwent a transurethral resection of the lesion. Morphologic and immunohistochemical findings suggested the diagnosis of pseudosarcomatous myofibroblastic proliferation. The patient is free of recurrence 5 years after surgery.