A 41-year-old woman with an incidental tumor of the urinary bladder was referred to our hospital. Computed tomography and magnetic resonance imaging showed a tumor in the urinary bladder wall with expansive growth. Under the suspicion of leiomyoma, we performed transurethral resection of the tumor. Pathological examination of tumor specimens revealed patternless arrangements of spindle cells. Immunochemical analysis revealed tumor cells positive for CD34 and bcl-2. The final diagnosis was a solitary fibrous tumor.