An asymptomatic 59-year-old man underwent pancreatoduodenectomy for a pancreatic mass that was discovered during a health check-up. Histopathology indicated typical features of lymphoplasmacytic sclerosing pancreatitis (LPSP) or autoimmune pancreatitis along with the presence of abundant IgG4-positive plasma cells throughout the mass. A small invasive ductal adenocarcinoma was observed in the center of the area affected by LPSP. The present case suggests that LPSP may be closely related to carcinogenesis of the pancreas.