Immunoglobulin G subclass 4 (IgG4)-related disease is a recently described fibroinflammatory condition. Reports of appendix involvement are extremely limited. A young man with abdominal pain and symptoms of acute appendicitis accompanied by the finding of an appendix-dependent tumor during surgery is presented. Histopathological study revealed lymphoplasmocytic infiltrate, storiform fibrosis and obliterative phlebitis. The number of IgG4-positive plasma cells was greater than 50 per high power field. Postsurgical steroid treatment and radiological findings are also described.