Recent research demonstrates that intergenerational differences in immigrant families' adaptation can be detrimental for family functioning. However, most of the findings originate from immigrant groups in North America who face different situations compared with European Diaspora returnees. This comparative study investigated whether ethnic German Diaspora immigrant adolescents' and mothers' disagreement about the desirability of adolescents' intercultural contact with native peers relates to more conflict in the family domain. In addition, we accounted for general developmental factors predicting family conflict by considering adolescents' background in terms of prosocial behaviour and hyperactivity. Participants comprised 185 Diaspora immigrant mother–adolescent dyads from the former Soviet Union living in Germany (adolescents: mean age 15.7 years, 60% female) and 197 native German mother–adolescent dyads (adolescents: mean age 14.7 years, 53% female). Results indicated a similar level of family conflict in immigrant and native families. However, conflict was elevated in those immigrant families disagreeing on intercultural contact attitudes, independent of the significant effects of adolescents' background of prosocial behaviour or hyperactivity. Our study highlights potential side effects in the family domain, if immigrant adolescents and parents disagree in their attitude regarding adaptation to the host culture's life domains, such as contact with native peers.