Are cohabiting couples more likely than married couples to break up in response to perceptions that their relationship is not fair? Based on social psychological perspectives on intimate relationship stability, in addition to empirical research contrasting cohabitation with marriage, I hypothesize that cohabiting couples will be more likely than married couples to separate in response to perceived breaches of justice. To test this hypothesis and others, I examine the influence of both male and female partners' perceptions of fairness on the stability of married and cohabiting couples using two waves of couple-level data from the National Survey of Families and Households. The results of Cox proportional hazards models suggest that cohabiting couples, but not married couples, are increasingly likely to separate as levels of male or female underbenefiting increase. The conclusion discusses the implications of these findings for social psychological perspectives and future studies on the role of distributive justice in the stability of intimate relationships. (Contains 3 figures, 2 tables and 7 footnotes.)