A 25-year-old patient with a rapidly growing sarcomatoid carcinoma of the urinary bladder is reported. The diagnosis was made on the basis of extended atypical proliferations of spindle or pleomorphic cells in the area of pelvic floor and the radix of the penis. The tumor showed invasion of the blood and a high Ki-67 growth fraction up to 40%. Immunohistochemically, the reactions with antibodies against cytokeratin, EMA, and vimentin were positive, while negative results were obtained in reactions with antibodies against desmin, actin, PSA, S 100, human epithelial antigen (Ber-EP4), and cytokeratin 13. The differential diagnosis against myosarcomas, pseudosarcomatous lesions, and inflammatory pseudotumours is discussed. After radical surgery a pelvic recurrence and pulmonary metastases developed, which led to the patient's death 3 months later. This case shows that sarcomatoid carcinomas of the urinary bladder can be found even in young people.