A 72-year-old woman with Mikulicz disease with pathogically proven sclerosing sialadenitis showed systemic abnormal F-18 FDG uptake in the bilateral lacrimal and submandibular glands, pancreas, abdominal aortic wall, and a retroperitoneal fibroid mass on PET/CT scan, with marked elevation of the serum IgG4 level. This case supports Mikulicz disease being included as 1 of the disorders associated with a new clinical entity of systemic IgG4-related plasmacytic syndrome. A whole-body FDG-PET/CT scan can be expected as a useful tool for detecting systemic involvement in systemic IgG4-related plasmacytic syndrome.