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We report five carcinomas of the urinary bladder, four of them transitional cell carcinomas and one undifferentiated carcinoma, with unusual features that have received little or no comment in the literature and may be the cause of diagnostic difficulty because of their possible confusion with malignant lymphoma. Four patients were male and one female. They ranged from 61 to 76 years of age. Three tumors from these patients had a prominent (2 cases) or massive (1 case) lymphoid infiltrate that partially obscured the invasive carcinoma in two cases and largely obscured it in the third case, which closely resembled a lymphoepithelioma. The diagnosis of malignant lymphoma was only excluded with confidence in the last case after thorough immunohistochemical study. The lymphoid infiltrate was composed of numerous T-cells (UCHL-1 and Leu 22 positive) and polytypic plasma cells with admixed eosinophils; occasional germinal centers were present in one case. The tumors were deeply invasive in two patients, one of whom is alive with no evidence of disease 4 years after treatment with chemotherapy and radiation therapy; the other two cases are too recent for meaningful follow-up. Two other transitional cell carcinomas had diffuse patterns that simulated lymphoma or plasmacytoma. Recognition of these patterns of vesical carcinoma is important in order to avoid the misdiagnosis of the very rare malignant lymphoma of the urinary bladder.