Inflammatory pseudotumor (IP) is generally considered to be a non-neoplastic, inflammatory response despite its gross and microscopic features of spindle cell neoplasm. Reported herein is a case arising from the muscularis propria of the urinary bladder in a 14-year-old girl who presented with gross hematuria and impending hypovolemic shock. The tumor consisted of proliferating myofibroblastic cells and various types of inflammatory cells. The immunoregulatory responses and reactions were investigated with regard to infiltration of inflammatory mononuclear cells being a documented finding in IP. Immunhistochemical and in situ hybridization studies for cytokines showed that the myofibroblastic cells were positive for interleukin (IL)-4, IL-5 and negative for interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha expression. The patient has been free of disease since excision of the tumor 34 months ago. Thus, cytokine production in IP suggests that it is reactive in nature and myofibroblasts may be the source of cytokines in the pathogenic process.