HOMINOID fossils from the Middle and Late Miocene are exceedingly rare, yet such material is necessary for determining hominoid phylogeny, We report here the discovery of a fossil hominoid partial skull from the Upper Miocene Sinap Formation(1,2) of central Turkey that is the most complete known from the period of 18 to 3 Myr. Our fieldwork places the hominoid locality within a precisely dated geochronological and biostratigraphical framework(3) that permits detailed comparisons with other fossil hominoids. Earlier discoveries of more fragmentary remains of Ankarapithecus meteai suggested affinities with the Asian hominoids Sivapithecus and Pongo(4). This new and nearly complete specimen reveals a combination of facial, mandibular, and dental features including a relatively narrow interorbital region, extensive frontal and maxillary sinuses, moderately developed supraorbital tori, square orbits, robust mandibular corpus, and incisor heteromorphy that is not matched in any extant or fossil hominoid. This configuration of features seems to support its placement as a stem member of the great ape and human clade.