BACKGROUNDImmunoglobulin G4-related disease (IgG4-RD) is an immune-mediated condition characterized by abundant IgG4 positive plasma cells and fibrosis in the affected tissues. It affects most parts of the body; however, there are not many reports on IgG4-RD involving the colon.CASE SUMMARYA 50-year-old man complaining of intermittent fever for more than two years was referred to our hospital. Based on various investigations before surgery, we diagnosed him with chronic perforation of the sigmoid colon caused by inflammatory change or tumor. IgG blood tests before the operation suggested IgG4-RD, and postoperative pathology confirmed this prediction.CONCLUSIONWe present a patient with IgG4-RD with colon involvement, which is an uncommon site. This report will expand the understanding of IgG4-RD in unknown tissues.