Small-cell neuroendocrine tumor is an aggressive and extremely rare cancer of the urinary bladder. The authors present a case of a 60-year-old man who was incidentally found to have a urinary bladder tumor on ultrasonography findings. He was then found to have an irregular mass in the right side of the urinary bladder based on cystoscopic and computed tomography examination. On pathological examination following resection of the tumor, the specimen was found to be a neuroendocrine small-cell subtype with muscularis propria invasion. He was then referred to the oncology department for further management.