The relative size of the cusps of the first mandibular molars of extant great apes and the Miocene hominoids, Proconsul and Sivapithecus were compared. As previously shown, molar morphology can differ between populations of the same species. Although the differences in crown size and shape are not as great as expected, each extant great ape species has a different overall design of the cusp base, probably reflecting its evolutionary history. The relative sizes of the cusps in Proconsul and Sivapithecus are different from those of any extant great apes.