We report a new case of Helicobacter pylori gastritis showing plasma cell infiltrates with extensive formation of Russell bodies (Mott cells) within the lamina propria of the antral mucosa. The patient was a 60-year-old woman with a history of epigastric pain. Endoscopy revealed non-specific congestion of the mucosa. Microscopically, the intracytoplasmic inclusions were homogeneous, mainly round to oval, and pushed the nucleus toward the periphery. They were intensely PAS-positive and reacted to antibodies against polytypic light chains, CD79a, and anti-plasma cell antibody. Because of the accumulation of intracytoplasmic inclusions, Russell body gastritis is a potential source of diagnostic difficulties in endoscopic biopsy specimens that can be confused with immunocytic neoplasms, such as lymphoplasmacytic lymphoma or plasmocytoma, or signet-ring cell carcinoma. In the light of similar cases published previously, it seems as if the association between Russell body gastritis and Helicobacter pylori infection is not merely coincidental.