A plasmacytoid variant of urothelial carcinoma has been recently recognized in the World Health Organization classification system. This is characterized by a discohesive growth of plasmacytoid cells with eccentric nuclei, extending in the bladder wall and often in the perivesical adipose tissue. Herein, we report the clinicopathologic, immunohistochemical, ultrastructural, and molecular features of a series of plasmacytoid urothelial carcinoma of the urinary bladder. Four bladder carcinomas characterized by epithelial cells with morphologic appearance resembling plasma cells were evaluated at the immunohistochemical, electron microscopic, and molecular genetic levels. Tumor cells stained with cytokeratins, epithelial membrane antigen, GATA-3 (endothelial transcription factor 3), CD15, p53, and p16. In addition, malignant cells strongly stained with CD138 in all the cases, whereas leukocyte common antigen and multiple myeloma 1/interferon regulatory factor 4 were completely negative, nor immunoreactivity was seen for either κ or λ light chains. The electron microscopic examination showed the presence of divergent squamous and glandular differentiation. At variance with conventional urothelial carcinoma, the analysis of exons 4-9 of TP53 gene revealed no alteration in all the 4 tumors tested, and this can be of value in choosing additional chemotherapy after surgery. Plasmacytoid carcinoma of the bladder is a tumor entity, which can be characterized by specific immunohistochemical markers, including positivity for GATA-3, and presents phenotypic and genotypic peculiarities.