We hereby report a case of diffuse pelvic peritoneal involvement by immunoglobulin G4-related disease (IgG4-RD). Numerous pelvic masses and nodules showing delayed enhancement on enhanced abdominal CT were found to congregate in the pelvic organs of a 57-year-old female presenting with intestinal subocclusion. The differentiation between peritoneal IgG4-RD and pelvic peritoneal carcinomatosis was only made by histopathology and immunohistochemistry performed after surgical resection. Autoimmune pancreatitis represents the historical prototype of IgG4-RD, but the spectrum of manifestations involving various organs has expanded during the last decade. In this report, we shortly review this clinical entity.