Plasmocytosis circumorificialis is a benign chronic inflammatory disease, which causes erythema, erosions, ulcers, nodules and related changes in and around the openings of the human body, and is histopathologically characterized by dense infiltration of the dermis by plasma cells. We recently encountered a 49-year-old man in whom this disease affected the lower lip. On initial examination in our department, a well-demarcated region of erosion (10 mm x 5 mm), accompanied in part by formation of a crust, was noted on the left side of his lower lip. Histopathologically, the mucosal epithelium exhibited erosions, and dense plasma cell infiltration, without signs of atypia, was noted in the upper through middle layers of the lamina propria. On the basis of these findings, plasmocytosis circumorificialis was diagnosed. Because the patient had experienced repeated cycles of remission and relapse, despite topical treatment with various drugs (e.g. topical antibiotics and steroids), prior to referral to our department, we administered topical 2% fusidate sodium or Fucidin (Leo Pharmaceutical, Ballerup, Denmark) ointment. His eruption healed approximately 3 weeks after the start of this treatment. We report this case and discuss the findings reported in Japan on the development of plasmocytosis circumorificialis of the lips.