The current paper examined associations between parenting and both peer group characteristics and friendship quality within a genetically sensitive design. Participants were aged 12-19 years (approximately equal numbers of males and females), including 424 sibling pairs and 1185 twin pairs, of whom 328 were MZ, 311 were DZ same-sex, 463 were DZ opposite-sex and 83 were of unknown zygosity. The adolescents provided self-report questionnaire measures of parental discipline, friendship quality, and peer group characteristics. All three relationship measures were moderately to substantially heritable. The novel and provocative finding, that adolescents' genetic propensities are largely responsible for the overlap seen between parental discipline strategies and friendship quality, is discussed in terms of its implications for socialization theory and understanding of adolescent relationships.