We tested a mediation model in which the relationship between child sexual abuse (CSA) severity and extradyadic sexual involvement (ESI) is explained through sexual compulsivity. Participants were 669 adults currently involved in an intimate relationship who completed self-report questionnaires. Prevalence of ESI was 32% in women and 57% in men survivors, more than twice the rates among participants with no CSA history. Sexual compulsivity was significantly higher in participants with multiple extradyadic partners as compared to participants reporting only one extradyadic relationship, who nevertheless scored higher than participants reporting no extradyadic partner. The hypothesized structural equation model (SEM) was invariant across men and women and indicated CSA severity was positively and significantly associated with sexual compulsivity, which, in turn, predicted ESI. However, there was also a direct association between CSA and ESI. High CSA severity, directly and through high sexual compulsivity, led to the highest probability of ESI.