We report a rare case of primitive neuroectodermal tumor/Ewing's sarcoma (PNET/ES) arising from the urinary bladder. A 65-year-old man presented with hematuria and dysuria. Computed tomography revealed an enlarged invasive tumor at the base of the bladder. No additional abnormal findings were disclosed by other diagnostic imaging methods. The surgical specimens showed small round cell tumor with positive staining for MIC2 gene product (CD99). EWS-FLI1 fusion transcripts were detected by reverse transcriptase polymerase chain reaction and direct sequencing, confirming the diagnosis of PNET/ES. The patient developed swollen pelvic lymph nodes as well as multiple lung metastases at 8 months postoperatively. No effective results could be obtained even with systemic chemotherapy consisting of vincristine, ifosfamide, doxorubicin and etoposide (VIDE) based on the EUROpean Ewing tumour Working Initiative of National Groups 1999 (EURO-E.W.I.N.G. 99) multinational trial. The patient died of acute superior mesenteric artery thrombosis at 22 months postoperatively. PNET/ES could have been included in past cases of small cell carcinoma because of the difficulty in its differential diagnosis. Exact diagnosis is crucial for deciding the treatment strategy for rare bladder tumors consisting of small round cells.