Parental relationship instability has led to an increase in families with children who have half- or step- siblings. This study uses Wave II and Wave III of the National Longitudinal Study of Adolescent to Adult Health, drawing from the sibling pairs sample (N = 1,753) to examine variations in sibling relationship quality (visit, calls/emails, emotional closeness, seeking help/advice, fights) across four sibling types – full biological (not twins), half, step, and twins – in young adulthood, while controlling for sibling relationship quality in adolescence. I find that full siblings report significantly better relationship quality compared to step siblings, but do not significantly differ in reports of relationship quality when compared to half siblings. Additionally, twins report more emotional closeness and help seeking than full siblings who are not twins. Time spent together and emotional closeness in adolescence significantly influenced all five aspects of sibling relationship quality in young adulthood.