There is limited research testing longitudinal models of how posttraumatic stress disorder (PTSD) severity leads to impaired relationship adjustment. The present study evaluated 2 potential mechanisms among a longitudinal sample of National Guard soldiers deployed to the Iraq War: (1) sensitivity to cues associated with punishment within intimate relationships and (2) sensitivity to cues associated with incentives in intimate relationships. Participants were surveyed by mail 1 year after an extended 16-month combat deployment and again 2 years later. Using a cross-lagged panel analysis with 2 mediators (relationship-specific threat and incentive sensitivity), findings indicated Time 1 PTSD symptom severity significantly eroded relationship adjustment over time through greater sensitivity to cues of relationship-related punishment, but not through incentive sensitivity. Additionally, findings indicated sensitivity to cues of relationship-related threats maintains symptoms of PTSD while sensitivity to cues of relationship-related incentives maintains relationship adjustment. Finally, PTSD symptoms significantly predicted erosion of relationship adjustment over time; however, associations from relationship adjustment to changes in PTSD severity over time were nonsignificant. Findings are discussed within the context of reinforcement sensitivity theory and emotional processing theory of PTSD.