Previous research shows a link between rejection sensitivity (RS) and various psychological disorders; however, its relation to the positive psychological construct of mental well-being remains unstudied. This study investigates the relationship between RS and mental well-being while taking the role of friendship quality into consideration for 323 emerging adults using decision tree analysis. In training (R 2 = .29) and test trees (R 2 = .18), RS had the strongest relationship with mental well-being where those higher in RS had lower mental well-being scores. For those lower in RS, higher combined (same-sex and opposite-sex) friendship qual-