Previous models of the risk of extramarital sex (EMS) rely largely on cross-section samples and retrospective reporting. This may well conflate causes with consequences of EMS in the same model. Instead, this study employs panel data with an event-history approach to re-assess the influences on the risk of EMS. The sample consists of 1,270 married respondents, with no prior history of EMS, who were followed up in five subsequent surveys spanning a 20-year period. The quality of the conjugal bond emerged as a paramount influence on the outcome. The hazard of EMS was higher for respondents who had ever experienced a trial separation, reported marital violence, scored higher on a marital instability index, or spent less time in activities with the spouse. The risk of EMS was lower the longer respondents had been married at baseline, the longer the duration since baseline, and the greater the respondent's religiosity.