--- - |2 Growing use of in vitro fertilization (IVF) has resulted in an elevated twin birth rate, and a burgeoning population of IVF twins who are now aging into adolescence and beyond. This study tests a model examining whether parental conformity expectations have differential effects on twins' versus singletons' parent–adolescent relationship satisfaction, and if this effect is indirectly associated with relative changes in twins' and singletons' internalizing and externalizing behavior from middle childhood to adolescence. Using a sample of 278 IVF twins and singletons, path models demonstrate that twin status and conformity expectations interact to influence parent–adolescent relationships. Although there was an association between twin status and mother–adolescent relationship satisfaction among parents with high conformity expectations (r = .25, p < .01), this relationship was nonsignificant among parents with low conformity expectations (r = .05, p = .85). The differential effect of conformity expectations on parent–adolescent relationship satisfaction for twins and singletons was indirectly associated with relative changes in twins' and singletons' externalizing behavior from middle childhood to adolescence. Results demonstrate that higher levels of parental conformity expectations may not have the same effect on adolescent twins and singletons. - Journal of Research on Adolescence, EarlyView.