Introduction: Using a prospective longitudinal design across six years, the current study investigated whether adolescents' experiences of peer rejection across middle school increased their risk of maladaptive (aggressive and unsupportive) behaviors in high school romantic relationships. Additionally, friendship quality following the transition to high school was examined as a potential protective factor. Methods: The sample consisted of 1,987 ethnically diverse youth (54% female; M age = 17.10) who were romantically involved at eleventh grade. Peer rejection (based on peer nominations) was assessed at four time points across three years in middle school. Students reported on their friendship quality in ninth grade and their aggressive (e.g., shouting; hitting) and supportive (e.g., listening; helping) behaviors towards a romantic partner in eleventh grade. Results: Results demonstrated that adolescents who were increasingly rejected by peers during middle school were more likely to behave aggressively towards their romantic partners in high school. Friendship quality at the beginning of high school moderated prospective links from rejection to support, such that escalating middle school peer rejection predicted less supportive romantic behaviors only among youth with low-quality friendships at ninth grade. These patterns were documented over and above the effects of sex, ethnicity, socioeconomic status, and students' aggressive behavior at the beginning of middle school. Conclusions: Together, the findings suggest that 1) increasing peer rejection during middle school may spiral into later romantic relationship dysfunction and 2) supportive friendships across a critical school transition can interrupt links between peer and romantic problems.Establishing healthy romantic relationships is considered a key developmental task of adolescence (Collins & van Dulmen, 2006;Furman, 2002), with the majority of teens reporting at least one romantic relationship by age 15 (Carver, Joyner, & Udry, 2003). Although early relationships provide opportunities for adolescents to experience companionship, intimacy, and support that offer preparation for healthy romantic bonds in adulthood, they can also present unique developmental challenges. In particular, adolescents' inexperience communicating with a romantic partner or managing the intense emotions of a romantic relationship can precipitate problematic interpersonal functioning. Indeed, up to 35% of adolescents exhibit aggression towards their dating partners (Haynie et al., 2013), and many young people feel ill-equipped to navigate romantic conflicts and foster caring intimate relationships (Weissbourd, Anderson, Cashin, & McIntyre, 2017). Because aggression and hostility in teenagers' romantic relationships are concerning developmental precursors to adult intimate partner violence (Exner-Cortens, Eckenrode, & Rothman, 2013), adolescence may