The clinical and pathologic features of three new and 35 previously reported carcinosarcomas of the urinary bladder were reviewed. This type of tumor is three times more common in men than women, and has occurred in patients from 33 to 82 years of age (average, 62 years), most of whom presented with hematuria of short duration. The tumors are usually large and polypoid, and on microscopic examination contain an intimate admixture of malignant epithelial and mesenchymal elements. The former may resemble transitional cell carcinoma, squamous cell carcinoma, adenocarcinoma or undifferentiated carcinoma; and the latter, fibrosarcoma, leiomyosarcoma, or undifferentiated sarcoma: skeletal muscle, osseous, and/or cartilaginous differentiation has occurred in from 25% to 50% of the tumors. Sixteen patients died as a result of their tumors; four others had metastatic disease and three were lost to follow-up. Twelve patients were alive and free of disease from 5 months to 7 years postoperatively. Most of the 12 underwent radical cystectomy, preceded in some cases by radiation therapy, but four underwent a more conservative operation.