Background: Uroplakin III is an asymmetric unit 47KDa glycoprotein present in the urothelial surface membranes of the human renal pelvis, ureter, bladder, and urethra. "The more poorly differentiated the urothelial cell, the lower the positive rate. About 60% of urothelial cell derived tumors (primary and metastatic) show focal (sometimes minimal) expression of Uroplakin III." The loss of Uroplakin III protein is usually associated with high tumor grade, invasion of muscular layer, and lymphatic metastasis. Our data suggest that Uroplakin III is specifically expressed in p63-negative urothelial tumors, including undifferentiated carcinoma; Paget's disease of the vulva associated with urothelial carcinoma can also be expressed.