Two hominin mandibles (KNM-BK 67 and KNM-BK 8518), as well as some postcranial remains (KNM-BK 63-66) were found between 1966 and 1982 on the west of Lake Baringo, northern Kenya, in the Middle Pleistocene sediments deposited along the Kapthurin River [1-4]. The two mandibles KNM-BK 67 and KNM-BK 8518 were found in the K3 Member of the Kapthurin Formation, at the Leakey Hominid Site and MAS locality, respectively. The sediments that yielded the two hominin mandibles are estimated to 512-510 ka [5]. The corpus of KNM-BK 8518 is recognized as being more robust than that of KNM-BK 67, but they are reported to share similar morphological features of the teeth (multirooted premolars, molarized P4, M3 with seven cusps and larger than M2) and have been regarded as likely belonging to the same taxon [2-3]. Based on the small dimensions and morphology of the mandibles, teeth and post-cranial remains, they have been regarded as falling outside the known variation of australopiths, and attributed to Homo sp. indet. (aff. erectus) [2-3]. In this study, we evaluate the current taxonomic affiliation of the Baringo mandibles based on new analyses of the mandibular corpus, dental arcade and internal structures of the preserved teeth. We use microtomographic imaging to investigate the external and internal morphology of teeth and bone and to characterize their taxonomy.