Küttner tumor/chronic sclerosing sialadenitis is a fibroinflammatory process that characteristically involves the submandibular gland of patients with IgG4-related disease. Histologic examination is often important to make the diagnosis because of its nonspecific clinical and radiologic findings. Microscopically, Küttner tumor should be distinguished from other entities such as extranodal marginal zone lymphoma, Sjögren's syndrome, and lymphoepithelial sialadenitis. The lesion is histologically well-demarcated with lobular architecture, extensive fibrosis, marked lymphoplasmacytic inflammation, formation of lymphoid follicles, acinar atrophy, and obliterative phlebitis, without the presence of lymphoepithelial lesions. The IgG4-to-IgG positive plasma cell ratio of >40 % is also an important feature to support the diagnosis of Küttner tumor. Moreover, flow cytometry is helpful to exclude a lymphoproliferative process. Clinicians and pathologists should consider the diagnosis of Küttner tumor in patients with elevated serum IgG4 level. Timely and accurate diagnosis is important for appropriate management.