Abstract Most theoretical models of sexual behavior among young people focus on “in-the-moment” decision-making processes. We focus on mid- and longer-term attitudes and preferences and how they influence sexual behavior in intimate relationships. We use the Relationship Dynamics and Social Life dataset (n = 952 women and 2,103 intimate relationships), based on a random sample of 18- and 19-year-old women in a Michigan county. We find that young women who are generally positive about young childbearing, who want large families, who prefer young motherhood, and who want to get pregnant in the near future spend more of the subsequent 2.5 years in intimate relationships, transition to sexual intercourse more quickly within those relationships, and subsequently have more frequent/regular sex throughout those relationships. We conclude that mid- and longer-term desires play a role in structuring women’s opportunity for sexual intercourse as well as their decisions about whether to engage in it.