IgG4-related disease (IgG4-RD) is now recognized as a worldwide disease. It is a rare systemic fibroinflammatory disorder. The evaluation for IgG4-RD should include a comprehensive clinical history, physical examination, and selected laboratory investigation, along with appropriate radiologic studies. A wide variety of organs can be involved in IgG4-RD. Confirmation of the diagnosis by biopsy is important for the exclusion of malignancy and other disorders that may mimic IgG4-RD. Consequently, diagnostic criteria for IgG4-RD have been proposed recently. The hallmarks of IgG4-RD are lymphoplasmacytic tissue infiltration of mainly IgG4-positive plasma cells and small lymphocytes, which may be accompanied by fibrosis, obliterative phlebitis, and, in the majority of patients, elevated serum levels of IgG4. The serum IgG4 level is elevated above the upper limit of normal (>135 mg/dL). The serum IgG4 concentration tends to increase with the number of organs involved and usually decreases after treatment with glucocorticoids. Among several autoantibodies identified so far, autoantibodies against lactoferrin and carbonic anhydrase II are most frequently detected in serum of IgG4-disease patients. Glucocorticoids, azathioprine, micophenolate mofetil, methotrexate and rituximab are therapeutical options.