CD138 (syndecan-1) immunoexpression has been reported to be specific for the plasmacytoid variant of urothelial carcinomas (UCs). The aim of this study was to examine the utility of CD138 immunohistochemistry for diagnosing the plasmacytoid variant of UCs. The extent and intensity of CD138 immunostaining were evaluated in 22 infiltrating UCs, 2 other infiltrating carcinomas, 15 noninvasive urothelial lesions, 3 other benign lesions, and perilesional normal tissues. CD138 immunostaining of the normal urothelial epithelium was universally diffuse and strong. In addition, all 42 cases of urinary tract lesions exhibited positive CD138 immunostaining; however, 1 of 3 plasmacytoid variants exhibited focal CD138 expression. The frequency of CD138 positivity in plasmacytoid variants may be relatively low, compared with that observed in the conventional types and other variants; thus, it is not appropriate to assume that CD138 expression in UCs is specific for plasmacytoid variants.