AbstractA postoperative spindle-cell neoplasm of the urinary bladder is an extremely uncommon lesion. The previous literature indicated that the neoplasm is an indolent, benign tumor and rarely exhibits clinically aggressive behavior. We report a 68-year-old male patient who underwent cystolithotomy for a huge urinary bladder stone. Two months later, he complained of progressively difficult micturition. Imaging studies revealed a huge invasive urinary bladder tumor, and a radical cystoprostatectomy with ileal conduit diversion was performed. The pathology report confirmed a spindle-cell tumor concomitant with a high-grade, papillary urothelial carcinoma. The patient recovered uneventfully, and there has been no tumor recurrence during ongoing follow-up (12 months).