A polyp of about 1.0 cm diameter was incidentally found at the center of the posterior wall of the urinary bladder in a 73-year-old man on cystoscopic examination. A polyp was resected through a transurethral route without recurrence for 22 months. A polyp consisted of a tumor covered with mucosa of the bladder. Tumor cells have round or oval nuclei with fine chromatin and one or two nucleoli per nucleus, and finely granular eosinophilic cytoplasm, being arranged in a trabecular or tubular pattern. Furthermore, they showed positive staining for chromogranin-A and with Grimelius stain, indicating that the tumor is a carcinoid tumor. Since there was no evidence of carcinoid tumors in organs other than the urinary bladder, the present case is a primary carcinoid tumor (well differentiated endocrine tumor) of the urinary bladder which is extremely rare.