Background and aims: Despite its high potential for affecting sibling relationships, few studies have explored the impact of the COVID-19 pandemic on this important family dynamic. Of these, the reported evidence has been inconsistent across cultures and lacks cross-cultural comparability. For the first time, we investigated cross-cultural variability in the impact of COVID-19, and the restrictions associated with it, on sibling relationships of autistic adolescents from a Western (United Kingdom) and non-Western (Turkey) country. We also explored how British and Turkish parents intervene in negative sibling interactions--that is, sibling bullying--when witnessed. Methods: Parents of 164 British and 96 Turkish autistic adolescents, aged 9 to 20 years, were asked how they perceived the effects of COVID-19 on their children's sibling relationships, and how they were most likely to react to instances of sibling bullying. Free response data from parents were analyzed using qualitative content analysis. Results: Our findings indicated more cross-cultural similarities than differences between British and Turkish families. The majority of both British and Turkish parents indicated that COVID-19 worsened sibling relationships between their autistic and nonautistic children. An overwhelming majority of British and Turkish parents also said that they would step in directly when witnessing sibling bullying. Despite the high volume of cross-cultural similarities generally, we also found some cross-cultural differences, for instance in relation to the most common negative impact of COVID-19 on sibling relationships and the most preferred parental responses to sibling bullying. Conclusions and implication: Implications and suggestions are discussed in more detail, drawing on the Etic approach to cross-cultural psychology.