Sibling sexual abuse is identified as the most common form of familial sexual abuse. Extant literature is plagued by definitional inconsistencies, data limitations, and inadequate research methodology. Trivialized as "normal" sexual exploration, sibling sexual abuse has been linked to psychosocial/psychosexual dysfunction. Research has relied on retrospective, convenience, and/or homogenous samples. This work drew on eight years of National Incident-Based Reporting System data (2000-2007) to provide aggregate level baseline information. This work extended prior research exploring victim-, offender-, and incident-based characteristics. Results highlight the need for expanded definitional criteria relating to both age and gender to better inform risk assessment and prevention. Findings both corroborate and contrast prior work and suggest victim- and offender-based gender differences. (Contains 5 tables and 1 footnote.)