The St. Cé saire 1 Neanderthal skeleton of a young adult individual is unique in its association with Châ telperronian artifacts from a level dated to ca. 36,000 years ago. Computer-tomographic imaging and computer-assisted reconstruction of the skull revealed a healed fracture in the cranial vault. When paleopathological and forensic diagnostic standards are applied, the bony scar bears direct evidence for the impact of a sharp implement, which was presumably directed toward the individual during an act of interpersonal violence. These findings add to the evidence that Neanderthals used implements not only for hunting and food processing, but also in other behavioral contexts. It is hypothesized that the high intra-group damage potential inherent to weapons might have represented a major factor during the evolution of hominid social behavior.Châ telperronian ͉ paleopathology ͉ tool use ͉ trauma ͉ computer tomography T he St. Césaire 1 Neanderthal partial skeleton was discovered in 1979 at the site of La Roche à Pierrot (near the village of St. Césaire, Charente Maritime, France), a collapsed rock shelter comprising a sequence of Mousterian, Châtelperronian, and Aurignacian deposits (1). The skeleton was recovered from level E J0P (1), which contains a Châtelperronian assemblage thermoluminescence-dated to Ϸ36,000 years ago (2, 3). This ensemble represented the first direct evidence for the association of Neanderthals with Châtelperronian implements. Together with a similar association from the site of Arcy-sur-Cure (4), these finds spurred an intense and ongoing debate over the evolutionary, paleodemographic, and cultural relationships between local Neanderthal populations and the early modern human (EMH) newcomers during the early Upper Paleolithic in Europe.The St. Césaire 1 skeleton is fragmented and partially eroded, but the reconstructed craniomandibular and long bone diaphyseal morphology permitted significant inferences regarding the phyletic status and behavioral specializations of this individual. The craniomandibular morphology of the specimen largely corresponds to the ''classical'' Neanderthal type (5). Tooth microwear analysis suggests a meat-rich diet comparable to that of earlier Neanderthals and modern hunting societies (6). The morphology of the well-preserved right femoral shaft indicates Neanderthal-type hyperarctic body proportions, but crosssectional biomechanical analysis suggests locomotor patterns closer to those of EMH than of classic Neanderthals (7).Here we report on recently discovered paleopathological aspects of the morphology of the fossil. During computerassisted reconstruction of the skull, we detected a healed fracture in the cranial vault. When paleopathological diagnostic standards (8, 9) are applied, this bony scar bears direct evidence for the impact of a sharp implement, which may have been directed toward the individual during an act of interpersonal violence. We discuss the possible behavioral context of this evidence and its implications for hominid behavior during the ...