A 28-year-old woman underwent renal transplantation in 1993. Eight years later, she experienced macroscopic hematuria, and Epstein-Barr virus-negative solitary extramedullary plasmacytoma (EMP) of the urinary bladder was diagnosed. After the reduction of immunosuppressive therapy, she received combined chemotherapy, resulting in complete tumor disappearance. However, 10 months later, she relapsed with aggressive multiple EMP and died of disease progression in 2003. This report is the first of a case of solitary EMP of the urinary bladder appearing as posttransplantation plasma cell dyscrasias after renal transplantation.