The aim of the present study was to examine whether adolescents of Moroccan and Dutch origin differ concerning sibling relationship quality and to examine whether the associations between quality of the sibling relationship and level and change in externalizing and internalizing problem behavior are comparable for Moroccan and Dutch adolescents. Five annual waves of questionnaire data on sibling support and conflict as well as externalizing problems, anxiety and depression were collected from 159 ethnic Moroccan adolescents (Mage = 13.3 years) and from 159 ethnic Dutch adolescents (Mage = 13.0 years). Our findings demonstrated significant mean level differences between the Moroccan and Dutch sample in sibling relationship quality, externalizing problems, and depression, with Moroccan adolescents reporting higher sibling relationship quality and less problem behavior. However, effects of sibling relationship quality on externalizing problems, anxiety, and depression were similar for the Moroccan and Dutch samples. Sibling support was not related to level of externalizing problems, nor to changes in externalizing problems, anxiety, and depression. Additionally, more sibling conflict was related to a higher starting level of and faster decreases in problem behaviors. Our results support the ethnic equivalence model, which holds that the influence of family relationships is similar for different ethnic groups. Moreover, sibling support and conflict affect both the level and the fluctuations in problem behavior over time in specific ethnic groups similarly. Implications for future studies and interventions are subsequently discussed.