IgG4-related disease is a systemic disease, characterized by elevation of serum IgG4 and, histopathologically, massive infiltration of IgG4+ lymphocyte and plasma cell infiltration, storiform fibrosis, causing enlargement, nodules or thickening. It may affect various organs simultaneously or metachronously. Here we analyzed the clinical and pathological characteristics of 99 patients diagnosed with IgG4-related periaortitis/periarteritis and retroperitoneal fibrosis. Of 99 patients (women/men, 15/84; mean age 67.3±9.5 years), 33 were diagnosed based on the histopathological findings of perivascular/retroperitoneal lesions, 50 were diagnosed based on the characteristic imaging findings of perivascular/retroperitoneal lesions and the presence of definitive IgG4-related disease in other organ(s), and the remaining 16 patients were diagnosed by experts based on the characteristic imaging findings of perivascular/retroperitoneal legions, serological findings, response to glucocorticoid treatment, and/or the presence of suspected IgG4-related disease in other organ(s). According to the new organ-specific criteria proposed by experts, 73 (73.7%) diagnoses were categorized to be definitive, and 6 (6.1%) and 17 (17.2%) diagnoses were categorized to be probable and possible, respectively. Further analyses are needed to clarify the optimal diagnostic and therapeutic strategy of IgG4-related periaortitis/periarteritis and retroperitoneal fibrosis. (This is a translation of J Jpn Coll Angiol 2018; 58: 117-129.).