Using a national sample of married (N = 752) and cohabiting (N = 323) couples, we examined the association between disillusionment and self-perceived breakup likelihood. Because disillusionment had not previously been studied in cohabiting couples, its extent and consequences for them were not known. We found considerable disillusionment in cohabiters, their mean level exceeding that of married couples. Based on a conceptual model of relationship change, we tested further whether disillusionment would predict self-perceived breakup likelihood, controlling for relationship satisfaction, commitment, and length. Furthermore, based on assumptions about barriers to leaving different types of relationships, we examined whether disillusionment’s association with breakup likelihood would be stronger in cohabiting than married couples. Results supported disillusionment’s ability to predict perceived breakup likelihood, even with rigorous controls, and the greater strength of this association in cohabiters. In addition, we found a significantly positive partner effect: Male partners’ disillusionment predicted female partners’ breakup likelihood.