Panel data from married adults (N = 1,853) in the General Social Survey, a probability sample of the adult household population of the United States, were used to evaluate (a) the longitudinal association between extramarital sex and marital dissolution 2 years later, (b) whether probability of marital dissolution differed as a function of the type of relationship people reported having with their extramarital sex partner, and (c) the degree to which these associations were incremental to participants’ level of marital satisfaction at baseline. Compared to people who reported not engaging in extramarital sex, those who reported engaging in extramarital sex at baseline were significantly more likely to be separated or divorced 2 years later. Furthermore, the association between having extramarital sex with a close personal friend and marital dissolution was particularly strong. These associations remained statistically significant after adjusting for marital satisfaction. Results suggest that the identity of the extramarital sex partner and the type of relationship a person has with him or her has important implications for probability of marital dissolution above and beyond the contribution of marital satisfaction.