The St. Césaire 1 Neanderthal skeleton of a young adult individual is unique in its association with Châtelperronian 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.