Russell bodies are globular and eosinophilic inclusion bodies in the cytoplasm of mature plasma cells.Plasma cells whose cytoplasm is filled with Russell bodies are designated as Mott cells.Russell body duodenitis(RBD) is a unique form of chronic duodenitis that is characterized by infiltration of numerous Mott cells.RBD is very rare;only two cases have been reported to date.In this paper,we report a case of RBD in a patient with retroperitoneal metastasis of ureteral cancer.A 77-year-old man was admitted to our hospital complaining of appetite loss,vomiting,and upper abdominal distension.He had undergone left nephroureterectomy for ureteral cancer 4 years earlier.Upper digestive tract endoscopy revealed edema,stenosis,and punctate redness of the mucosa of the duodenum,and a biopsy was performed.Histological analysis showed that numerous Mott cells had infiltrated the lamina propria mucosae,and the condition was diagnosed as RBD.A mass lesion in the retroperitoneum adjacent to the duodenum was detected by abdominal computed tomography,and was diagnosed as metastatic urothelial carcinoma by biopsy.It is possible that chemokines produced by tumor cells caused RBD in this case. Russell bodies are globular and eosinophilic inclusion bodies in the cytoplasm of mature plasma cells. Plasma cells whose cytoplasm is filled with Russell bodies are designated as Mott cells. Russell body duodenitis (RBD) is a unique form of chronic duodenitis that is characterized by infiltration of numerous Mott cells.RBD is very rare; only two cases have been reported to date. in this paper, we report a case of RBD in a patient with retroperitoneal metastasis of ureteral cancer. A 77-year-old man was admitted to our hospital complaining of appetite loss, vomiting, and upper abdominal distension. He had undergone left nephroureterectomy for ureteral cancer 4 years earlier .Upper digestive tract endoscopy revealed edema, stenosis, and punctate redness of the mucosa of the duodenum, and biopsy was performed. Histological analysis showed that numerous Mott cells had infiltrated the lamina propria mucosae, and the condition was diagnosed as RBD. A mass lesion in the retroperitoneum adjacent to the duod enum was detected by abdominal computed tomography, and was diagnosed as metastatic urothelial carcinoma by biopsy. It is possible that that chemokines produced by tumor cells caused RBD in this case.