A longitudinal analysis is conducted on the union quality of long-term cohabiting and legally married couples using data from both waves of the National Survey of Families and Households. An analysis of racially homogamous (Anglo-American and African American) couples indicates that the cohabitors and marrieds do not differ significantly with regard to their frequency of conflict, perceptions of equity, and relationship satisfaction, although age, educational attainment, and educational homogamy affect differentially the cohabitors' and marrieds' perceptions of equity with time, and the cohabitors' satisfaction in particular is negatively affected by the number of children biologically related to both partners. Cohabiting couples initially spend more time alone together than do married couples but with time come to resemble the marrieds. The union quality of cohabiting and married couples is affected in the same way by union duration and prior residential union experience.