The Middle Period in San Pedro de Atacama (AD 400–1000) stands out as a time of great prosperity that was, in part, associated with high levels of interaction with foreign polities, including the highland state of Tiwanaku. Although previous studies have demonstrated an increase in rates of violence during the subsequent Regional Developments Period (AD 1000–1400), this does not mean that the Middle Period was a time of peace and tranquility. Here, the prevalence of violence in four contemporary cemeteries is analyzed, exploring potential sources of conflict, including social inequality. Cranial trauma was documented through the presence, location, size, and state of healing of all wounds and was found in 14.7% of the sample (61/415; including two cases of perimortem trauma). Skeletal remains were also analyzed for demographic data to investigate differences in patterns of violence related to sex and age. Notably, most of the trauma centered on the anterior portion of the skull, suggesting the prominence of face-to-face confrontations that involved both sexes. Correlations between trauma and items in the mortuary assemblage that may have been associated with prestige or an elevated social standing in two cemeteries from the Solcor ayllu indicate that individuals from the more elite cemetery were subjected to significantly less traumatic injury. These data suggest that people did not share equally in the benefits of this period's affluence and that there were tensions in Atacameño society despite seemingly widespread prosperity. Am J Phys Anthropol, 2011. © 2011 Wiley-Liss, Inc.