While rescription-based therapies are effective treatments for chronic post-trauma nightmares, mechanisms of change have not yet been defined. We examined the relationship between the use of cognitive-related words in nightmare narratives and the posttraumatic cognitions inventory (PTCI) in a sample of 25 trauma-exposed individuals undergoing rescription therapy for post-trauma nightmares. In addition to exploring the relationship between different types of cognitive language use and PTCI scores, the relationship between changes in their frequency of use and posttrauma cognitions were also analyzed. We found that cognitive language use as a whole in addition to the subcategories of tentative, discrepancy, and insight words within the nightmare are significantly negatively related to baseline PTCI scores, while analytic language use was positively correlated. However, cognitive language use in the rescription did not relate to PTCI scores post-treatment. Furthermore, changes in the of use cognitive language, between the nightmare and the rescription, are significantly negatively associated with severity of posttraumatic cognitions at the post-assessment. These results demonstrate the importance of understanding cognitive language in nightmare imagery as it may relay important information about treatment outcomes.