Sibling relationships can have an important effect on a child's development, and siblings impact each other in a variety of ways. Although prior research has examined the ways in which sibling relationship quality impacts various outcomes, few studies have examined older adolescents, ethnic minorities, and positive outcomes. Thus, the goals of this research were to investigate the influence of sibling relationship quality on both positive and negative outcomes, to examine these influences in middle adolescence, to investigate the ways in which sibling relationship quality and adolescent outcomes are related in both European- and Mexican-American adolescents, and to explore the possibility that strong family values, as captured by familism, might moderate the relationship between sibling relationship quality and adolescent outcomes.

In order to investigate these goals, adolescents responded to a questionnaire that asked them to report on their relationship with their sibling closest in age, their familism values, and a variety of outcomes. Parents and teachers also reported on adolescents' internalizing and externalizing behavior problems as well as their positive behaviors. Consistent with the hypotheses, sibling conflict was positively related to risky sexual behaviors, substance use, and internalizing and externalizing behavior problems, and sibling support was negatively related to risky sexual behaviors and externalizing problems. However, although sibling relationship quality was not consistently related to positive outcomes, familism was importantly related to positive outcomes. Additionally, there were no significant differences between European- and Mexican-American adolescents in the way in which sibling relationship quality was related to outcomes. Furthermore, this study found that familism had a main effect on positive outcomes, but a moderating impact on negative outcomes. In sum, this study has added to the sibling relationship literature by extending the age ranges studied, as well as by examining the possibility of different cultural influences, although none were found. Also, this study has helped to identify the ways in which sibling relationship quality impacts both positive and negative adolescent outcomes, and has discovered a promising new area of research involving the impact that family type has on the quality of the sibling relationship and adolescent outcomes.