A case of an inflammatory pseudotumor of the urinary bladder in a 46-yr-old man is presented. This rare, benign, and presumed non-neoplastic, reactive lesion must be differentiated from sarcomas of the urinary bladder. In the present case, we could demonstrate an inflammatory and reactive nature for the pseudotumor. Histologically, the presence of many Brunn's nests with infiltration of inflammatory cells and proliferation of capillaries in the myxoid stroma indicated a chronic inflammatory background for this lesion. It is apparent from morphology and immunohistochemistry findings that the proliferating spindle-shaped cell is of mesenchymal origin and not malignant in nature. These findings suggest that chronic inflammation can induce an overreaction of the bladder wall resembling tumor formation.