IgG4 related disease (IgG4 RD) was first reported as autoimmune pancreatitis then it was established as a systemic disorder characterised by high blood level of IgG4 and fibrosis with rich plasmocytes IgG4+ in almost all organs. IgG4 RD is very sensitive to corticosteroid therapy. IgG4 RD has a high prevalence in eastern countries. Numerous articles on this topic are published and new diagnostic criteria are regularly established. The autoimmune or allergic mechanism of IgG4 RD is still a matter of debate. Interestingly, IgG4 subclass of antibody has anti-inflammatory features. IgG4 RD is not yet very well characterised in western countries. Whether IgG4 is involved in IgG4 RD, pathophysiology is to be defined. IgG4 RD spontaneously regresses in some cases so indications of treatment are not already well clear.