Siblings describe positive and negative aspects of autism and often assume lifelong support roles. Less is known about cultural influences on sibling relationships. This qualitative study characterizes processes linking siblings' autism conceptualizations, sibling relationships, and self-concept using a multicultural framework. Siblings (12 Latino/a/x, 9 non-Latino/a/x white) participated. Data were stratified by ethnicity and analyzed using applied thematic analysis. Latino/a/x and non-Latino/a/x siblings described processes linking autism, relationships, and self-concept differently. Latino/a/x siblings emphasized family roles and identified as caregivers and protectors. Non-Latino/a/x siblings emphasized general sensitivity toward individuals who differed from themselves. Findings may reflect cultural differences in familism, caregiving expectations, and autism conceptualizations, thereby illuminating foundations of siblings' lifelong caregiving roles and highlighting the importance of culturally-sensitive, family-centered care.