Sialadenoma papilliferum (SP) is a rare, benign, salivary gland tumor which most commonly arises in the palate. It has a typical biphasic gross and microscopic appearance which distinguishes this tumor from other papillary-like tumors of the oral cavity. This study reports the clinico-pathologic features of 5 new cases and analyzes the morphologic and immunophenotypic features of their cell components. Adluminal epithelial cells of duct-like structures appeared immunoreactive to cytokeratin 19 and to S-100 protein antibodies; two subsets of basally-located cells were identified by means of immunohistochemistry. One cell subset expressed cytokeratin 14, S-100 protein, GFAP, vimentin and smooth muscle actin immunoreactivity; this antigenic profile is consistent with myoepithelial differentiation. The second subset of basal cells expressed cytokeratins 13 and 14 reactivity but it was negative to all other antibodies. Anti-CD 1a and anti-S-100 protein antibodies revealed distinct cells with dendritic processes which resembled Langerhans cells. The extralobular location of SP, the continuity between neoplastic duct-like structures and the surface epithelium along with the presence, within the excretory ducts adjacent to the tumour, of lesions which possibly precede the development of SP give further strength to the hypothesis of an origin from the excretory ducts of this tumor. Langerhans cells seem to be present in sialadenoma papilliferum but their role in this tumor is still unclear.