Lymphoid proliferations of the salivary glands can be either reactive or neoplastic. Reactive lesions include cystic lymphoid hyperplasia--a multicystic ductal proliferation with reactive germinal centers, seen most often in intravenous drug users infected with HIV--and the lymphoepithelial sialadenitis of Sjögren's syndrome (so-called benign lymphoepithelial lesion [BLEL] or myoepithelial sialadenitis [MESA]). This lymphoid proliferation involves infiltration of ductal epithelium by lymphocytes of marginal zone or monocytoid B-cell type, forming lymphoepithelial lesions (epimyoepithelial islands). Patients with lymphoepithelial sialadenitis have a 44-fold increased risk of developing salivary gland or extrasalivary lymphoma, of which 80% are marginal zone/MALT type. Broad strands of marginal zone or monocytoid B cells around lymphoepithelial lesions and monotypic immunoglobulin detection by immunohistochemistry are considered diagnostic of MALT lymphoma. B-cell clones are detected in over 50% of cases of MESA by molecular genetic methods, but this does not correlate with overlymphoma. "Nodal" type B-cell lymphomas of the salivary glands are either follicular lymphoma (35%), which may arise in intrasalivary gland lymph nodes and behave similarly to follicular lymphoma in other sites, or diffuse large B-cell lymphoma (30%), which may arise de novo or secondary to either MALT or follicular lymphomas.