The formation and maintenance of young adult romantic relationships that are free from violence and are characterized by love, connection, and effective problem-solving have important implications for later well-being and family functioning. In this study, we examined adolescent hostile-aggressive behavior (HAB) and family relationship quality as key individual and family level factors that may forecast later romantic relationship functioning. Guided by a family systems framework, we evaluated the reciprocal influences of adolescent hostility and family climate, to provide a more comprehensive picture of the etiology of romantic relationship functioning. We drew on a large sample (N = 974) of young adults (mean age = 19.5) that were followed starting in the fall of 6th grade, and subsequently in spring of 6th, 7th, 8th, 9th, and 10th grades prior to the young adult assessment. Using a latent difference score cross-lag model (McArdle, 2009), our results indicated that a more positive family climate was associated with decreases in HAB, but HAB was not associated with changes in family climate. Further, the influence of the family climate on HAB was consistent across all time points. HAB and family climate had different predictions for young adult romantic relationships: Increasing HAB over adolescence predicted relationship violence, while maintenance in family climate was a key predictor of relationship problem-solving skills. The only predictor of love and connection in relationships was early family functioning. Implications for developmental theory and prevention science are discussed. (PsycINFO Database Record