<p>Siblings of children with neurodevelopmental disorders (NDD) are often exposed to challenging behaviors from their neurodivergent siblings, which may be associated with persistent negative feelings. While social support has been shown to buffer the effects of such challenges, limited research has examined emotional responses in these siblings. This study explored the association between discomfort caused by challenging behaviors and persistent negative feelings toward children with NDD, and investigated whether perceived social support moderates this association. A self-report questionnaire was completed by 127 siblings of children with NDD. Three scales were developed to assess discomfort with challenging behaviors, persistent negative feelings, and perceived social support from fathers, mothers, friends, and teachers. A significant correlation was found between discomfort and persistent negative feelings. Perceived social support moderated this association, such that higher levels of support were linked to lower levels of negative feelings—although the buffering effect was weaker when discomfort levels were high. These findings suggest that social support may play a protective role in the context of sibling emotional adjustment, particularly when discomfort is less intense.</p>