The patient was a 75 year-old male. Noticing areas of hardening in the lower abdomen, and consequently feelings of systemic fatigue and difficulty in walking, the patient visited a clinic and was diagnosed with kidney failure prior to the visit to our clinic. Computed tomography and magnetic resonance imaging showed thickness of the rectus abdominis muscle and the bladder wall, and bilateral hydronephrosis was also identified. As no explicit tumor was identified in the bladder, the patient underwent biopsies of the abdominal wall and bladder membrane mucous, and was diagnosed with a plasmacytoid urothelial carcinoma primarily developed in the bladder. The patient displayed a poor general state of health and died five months after the diagnosis. It is known that plasmacytoid urothelial carcinomas progress rapidly and the prognosis is poorer than for the micropapillary variant. It is important to obtain a tissue specimen in the early stage of this disease because there are cases in which no explicit tumor can be identified. Furthermore, the value of carbohydrate antigen (CA) 19-9 of the patient was much higher than would be expected as normal at the first visit. It kept rising during the follow-up and was useful as a marker to indicate the progress of the disease.