Among benign proliferations of the urinary bladder, von Brunn nests and cystitis cystica et glandularis are common. Sometimes florid proliferation of von Brunn nests makes an intravesical mass, which mimics tumorous lesions. We report here on a case of florid von Brunn nests, occurred in the 34-year-old man with hematuria. Radiological and cystoscopic examinations reveal a polypoid-papillary lesion and transurethral resection was then performed. Pathologically, prominent proliferations of urothelial cell nests were found deep in the lamina propria. Neither significant cytologic atypia nor muscle invasion was noted. Florid von Brunn nests should be considered both clinically and pathologically in the differential diagnosis of a intravesical mass.