Identified as a social problem in 1980, sibling violence has been labeled the most common and least researched form of family violence in the United States (Eriksen and Jensen 2006, 2008). Extant research has limitations including definitional inconsistencies, overreliance on small retrospective clinical samples, and limited use of officially reported national level data for profiles of victims and offenders. Although often trivialized as a "normal" part of growing up, sibling violence has links to an array of complications manifesting later in life including physical and emotional disorders, school bullying, substance abuse, and domestic violence. This work draws on 6 years of National Incident-Based Reporting System (NIBRS) data (2000-2005) (n=33,066) to provide the most comprehensive source of baseline information on this understudied form of intrafamilial violence. The research explores demographic and incident characteristics extending the knowledge beyond typical victim descriptives to incorporate offender profiles and incident level information including the type of violence/victimization, substance use, weapon use, and degree of injury sustained. Findings, in part, suggest several gender based victim and offender differences with female siblings involved in more serious injury incidents than their male sibling counterparts. (Published Abstract)