IgG4-related disease is a recently recognized fibroinflammatory disorder characterized by extensive IgG4-positive plasma cell and lymphocyte infiltration of various organs. The pancreatic manifestation of IgG4-related disease is called autoimmune pancreatitis (AIP), in which autoimmune mechanisms are likely involved. On the other hand, some autoimmune and chronic inflammatory disorders, such as Sjögren's syndrome and rheumatoid arthritis, are associated with increased risks of non-Hodgkin lymphoma (NHL). There have been a few reports of cases with IgG4-related disease that had subsequently developed NHL, however, all of them suffered from B-cell lymphoma. We describe the first case of NHL, compatible with a subtype of peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), which arose in IgG4-related sclerosing cholangitis. As patients with IgG4-related disease may be at an increased risk of developing NHL, such presentation during the follow-up of IgG4-related disease should be carefully scrutinized to exclude NHL.