Recent evidence from Canada and Sweden indicates that cohabitation prior to marriage significantly increases the risk of subsequent marital dissolution. In this article we present results testing the hypothesis that cohabitation increases marital disruption in the United States. We find that premarital cohabitation increases the risk of subsequent marital instability. However, the effect of cohabitation can be attributed to the fact that cohabitants have spent more time in union than noncohabitants. Once total length of union is accounted for, there is no difference in marital disruption between cohabitants and noncohabitants. We argue that subsequent research comparing cohabitants and noncohabitants with respect to marital behaviors that are duration dependent should account for the total amount of time spent in union.