To better understand the social factors that influence the diverse pathways to family formation young adults experience today, this research investigates the association between opposite-gender relationships during late adolescence and union formation in early adulthood. Using data from the first and third waves of the Add Health (n=4,911), we show that, for both men and women, there is continuity between adolescent and adult relationship experiences. Those involved in adolescent romantic relationships at the end of high school are more likely to marry and to cohabit in early adulthood. Moreover, involvement in a nonromantic sexual relationship is positively associated with cohabitation, but not marriage. We conclude that the precursors to union formation patterns in adulthood are observable in adolescence.