Background: Typically developing (TD) siblings of individuals with autism spectrum disorder (ASD) often fulfil caregiving roles as children or adults (i.e., parentification, which can be either parent-focused or sibling-focused).Method This study examines how parentification interacts with social support when predicting distress and sibling relationship attitudes in 60 TD adult siblings of individuals with ASD. Results: Perceived social support served as a moderator. Specifically, TD adult siblings who experienced high parent-focused parentification during childhood and low current social support were most likely to report high distress. TD siblings who reported low sibling-focused parentification during childhood and low current social support were most likely to report less positive attitudes about their relationships with their siblings with ASD. Conclusions: Current findings suggest that perceived social support may serve as a potential point of intervention for reducing distress and improving sibling relationship attitudes among adult TD siblings of those with ASD.