Extradyadic sex and union dissolution among young adults in opposite-sex married and cohabiting unions

• Among married and cohabiting young adults, 1 in 4 report extradyadic sex (EDS).
• Men self-report EDS more than women, women report partner's EDS more than men.
• Partner's EDS is associated with union dissolution, respondent's own EDS is not.
• Links between EDS and union dissolution do not vary for cohabiters and spouses.
• Links between EDS and union dissolution do not vary by gender.

This study investigates extradyadic sex (EDS) among contemporary opposite-sex married and cohabiting young adults and examines how EDS is associated with union dissolution. By analyzing data from 8301 opposite-sex spouses and cohabiters in the National Longitudinal Study of Adolescent to Adult Health, we estimate the prevalence of self-reported EDS, reports of partners' EDS, and reports of mutual EDS (i.e., both partners' engagement in EDS). Roughly 1 in 4 respondents reported that either they, their partner or both engaged in EDS. Young men were more likely than women to self-report EDS, while young women were more likely to report partners' EDS. Relative to no EDS, partners' EDS was associated with union dissolution, but self-reported EDS and mutual EDS were not. A partner's EDS was also associated with union dissolution relative to self-reported EDS. Associations between a partner's EDS and dissolution were consistent among spouses and cohabiters and among men and women.