In our patient, we firstly suspected lung cancer that spread to multiple lymph nodes and to the pancreas, but histologic examinations of the lung nodule were not diagnostic. Based on the positive antinuclear antibody, the elevated serum IgG level, and the radiographic findings, we next considered IgG4-related sclerosing disease in the differential diagnosis and measurement of IgG4 as a diagnostic study. However, elevated levels of IgG4 have been reported in pancreatic cancer, and the patient requested a definite diagnosis. So we decided to perform a surgical biopsy of the pancreas. The histologic findings were consistent with lymphoplasmacytic sclerosing pancreatitis. We further performed immunostaining and detected aggregates of IgG4-positive plasma cells in the biopsy samples from both the lung and pancreas. The serum IgG4 level turned out to be increased (996 mg/dL; normal, 4.8-105). Consequently, the patient fulfilled the diagnostic criteria for autoimmune pancreatitis, and a convincing diagnosis of systemic IgG4-related sclerosing disease was made.