The types of appraisals that follow traumatic experiences have been linked to the emergence of posttraumatic stress disorder (PTSD). Could changing reappraisals following a stressful event reduce the emergence of PTSD symptoms? The present proof-of-principle study examined whether a nonexplicit, systematic computerized training in reappraisal style following a stressful event (a highly distressing film) could reduce intrusive memories of the film, and symptoms associated with posttraumatic distress over the subsequent week. Participants were trained to adopt a generally positive or negative poststressor appraisal style using a series of scripted vignettes after having been exposed to highly distressing film clips. The training targeted self-efficacy beliefs and reappraisals of secondary emotions (emotions in response to the emotional reactions elicited by the film). Successful appraisal induction was verified using novel vignettes and via change scores on the post traumatic cognitions inventory. Compared with those trained negatively, those trained positively reported in a diary fewer intrusive memories of the film during the subsequent week, and lower scores on the Impact of Event Scale (a widely used measure of posttraumatic stress symptoms). Results support the use of computerized, nonexplicit, reappraisal training after a stressful event has occurred and provide a platform for future translational studies with clinical populations that have experienced significant real-world stress or trauma.