Objective: Solitary fibrous tumor (SFT) is an unusual spindle cell neoplasm, which can exceptionally occur in the urinary bladder. Method: We present a case of urinary bladder SFT in a 60 year-old man who complained of pelvic pain. Cystoscopy revealed a large protruding, fleshy mass at the anterior wall of the bladder. A biopsy was first misclassified as inflammatory myofibroblastic tumor (IMT). Subsequent complete transurethral resection was performed. Results: Macroscopically, a 9×7×5 cm greyish lobulated firm polypoid tumor was seen. Microscopically, it consisted of uniform spindle cells with elongated tapered ends nuclei forming a patternless growth in a collagenous background. Mitotic figures were rare. Immunohistochemically, the neoplastic cells were positive for CD34 and bcl-2, and negative for α-SMA, desmin, CK AE1/ AE3 and Alk-1. The bladder urothelium showed foci of high-grade transitional carcinoma with lamina propria invasion. Conclusion: Initially, SFTs were thought to be of mesothelial origin. Then, these tumors have also been observed in extrapleural and extraserosal sites, which suggests a mesenchymal cell origin. The differential diagnosis should always include other spindle cells lesions such as sarcomatoid carcinoma, leiomyosarcoma and IMT. To date, this is the first reported case of association of urinary bladder SFT and high-grade urothelial invasive carcinoma.