Background: Having a child with intellectual disability impacts all family members, with both parents and siblings having to adjust. Negative impact on the typically developing sibling, specifically, has been shown to vary based on caregiving responsibilities and mothers' stress level. Method: This study gathered information from 238 Latina and Anglo mothers of young adults with intellectual disability to explore sibling negative impact related to maternal stress, positive feelings about parenting, sibling diagnostic category, and cultural group. Results: Mothers experiencing more stress reported higher levels of sibling impact; mothers with more positive feelings about parenting reported lower levels of negative impact, with Latina mothers reporting higher levels of stress and positive feelings about parenting. Anglo mothers, however, were less likely to designate a sibling as a future caregiver. Conclusions: These findings suggest culture and diagnostic classification should be given more attention relative to their impact on typically developing siblings.