To determine whether recent birth cohorts of women experienced more union dissolution during young adulthood (18-25) than previous birth cohorts. The union formation and dissolution patterns of young adult women in the U.S. have changed dramatically over the last twenty-five years. As a result, this life stage is demographically dense as women experience a bulk of relationship experiences, including coresidential unions and dissolution. The author uses data on women's marital and cohabiting dissolutions between the ages of 18-25 from the National Survey of Family Growth 1995, 2002, and continuous surveys 2006-2010 and 2011-2015 (N = 14,211). The sample is nationally representative. The author uses generalized ordinal logistic regression to examine the likelihood of dissolution during young adulthood across birth cohorts. Women born between 1985 and 1989 experience more union dissolutions during young adulthood than women born between 1960 and 1979. However, the shift in cohabitation behavior accounts for this instability. Women's relationship formation experiences in young adulthood are characterized by nonmarital relationships (cohabitation) and more union dissolution compared to older birth cohorts. Theoretical and empirical studies need to evolve to include this more complicated sense of young adulthood, union formation, and instability.