This study examined sibling relationship qualities as predictors of romantic relationship characteristics in late adolescence and tested adolescent and sibling gender constellation as potential moderators of these linkages. In home interviews, 125 White working- and middle-class adolescents (M = 16.52, SD = 0.77 years old at Time 1) reported on sibling relationship intimacy, conflict, and control, and 2 years later they reported on intimacy and their relative power in their romantic relationships. Sibling intimacy was a positive predictor of relative romantic power, and sibling conflict was a negative predictor of romantic intimacy, but only for girls. Sibling control positively predicted romantic intimacy and, for mixed-gender sibling dyads, also predicted relative romantic power. Discussion focuses on the role of siblings in romantic relationships and directions for future research.