RESUMEN
Prevalence estimates of sibling bullying indicate it occurs more frequently and with more negative consequences than peer bullying, yet many countries do not track or investigate the phenomenon. University students from Argentina, Estonia, and the United States were surveyed to investigate their retrospective experiences involving sibling bullying, how often it occurred, the roles held, and the forms communicated. In the aggregated data, roughly 50 % of the sampled emerging adults (N = 3477) reported experience with sibling bullying, with the dual role of bully-victim being the most frequently reported role held by males and females, with the second role being bully for males and victim for females. Verbal forms of bullying were most frequently reported by males and females, with physical, relational, and technological forms occurring less frequently, indicating the importance of studying the messages conveyed during bullying incidents. Variations between biological sex, bullying role and form were detected that indicate siblings experience bullying in ways that are unique from peer bullying. Country comparisons revealed bullying frequencies varied among males and females, suggesting sibling bullying experiences are likely to be culturally influenced. More research is warranted to examine the negative impact bullying has on sibling psycho-social development and the potential transfer to non-familial relationships and contexts. Discussion of these findings and the implications for academics and practitioners alike is provided.