Intimate partners experience more negative emotion in response to sexual versus nonsexual conflicts in their relationship. Negative emotions hinder communication and sexual well-being. In a laboratory-based observational study, we tested the prediction that couples who took longer to downregulate negative emotion during a sexual conflict discussion would report lower sexual well-being. Long-term couples (N = 150) were video recorded while they discussed the most contentious problem within their sexual relationship. Participants subsequently viewed their filmed discussion and used a joystick to continuously report on their emotional experience during their disagreement. Trained coders continuously coded the valence of participants' emotional behavior. Downregulation of negative emotion was assessed by calculating how quickly, on average, an individual's negative emotional experience and behavior returned to neutral during their discussion. Participants also completed measures assessing sexual distress, satisfaction, and desire prior to the discussion and 1 year later. Analyses were conducted per the Actor-Partner Interdependence Model. For both women and men, we found that a person's slower downregulation of negative emotional experience was concurrently associated with their own greater sexual distress and lower sexual desire and with their partner's lower sexual satisfaction. Downregulation of negative emotional experience also predicted one's own lower sexual satisfaction and, surprisingly, higher sexual desire for both members of the couple 1 year later. People who took longer to downregulate their negative emotional behavior during the conflict also reported higher sexual desire 1 year later. Findings suggest that greater difficulty shifting out negative emotional states during sexual conflict is concurrently linked with poorer sexual well-being for long-term couples.