Mental contamination-an internal experience of dirtiness evoked in the absence of physical contact with an external source-has been linked to the development and maintenance of posttraumatic stress disorder (PTSD) following exposure to sexual abuse or assault (Adams et al., 2014; Badour et al., 2013; Brake et al., 2017). Mental contamination has been associated with greater PTSD severity (Rachman et al., 2015) and higher elevations in specific PTSD symptom clusters (particularly those of intrusive re-experiencing, negative cognitions/mood, and arousal/reactivity; Brake et al., 2019; Fergus \& Bardeen, 2016). Additionally, trauma-related mental contamination has been linked to a number of negative posttraumatic emotions such as shame, guilt, disgust, and anger (Fairbrother \& Rachman, 2004; Radomsky \& Elliott, 2009). Despite clear and consistent links between mental contamination and problematic posttraumatic outcomes following sexual trauma, there is a dearth of research investigating how existing or promising new interventions for PTSD impact mental contamination. Written Exposure Therapy (WET) is a five-session treatment for PTSD that was designed to be both brief and easy to administer (Sloan et al., 2012). According to Sloan and colleagues' (2012) protocol, sessions broadly involve 30-minute exposures in which the patient writes about the events of their trauma in detail, followed by 10 minutes of discussing the exposure with the therapist. This treatment protocol has minimal therapist involvement, no homework assignments, and shorter treatment sessions. Research shows that WET is efficacious among different samples (e.g., survivors of motor vehicle accidents and combat veterans), has low dropout rates, treatment satisfaction is high, and the gains seen by participants after completion are maintained at follow-up (Sloan et al., 2012, 2013, 2018; Thompson-Hollands et al., 2018, 2019). Given these factors, WET has the potential to be a useful intervention in reducing symptoms of PTSD among a sample of survivors of sexual trauma. Given its relevance to this trauma population, a test of this intervention for its impact on reducing trauma-related mental contamination is also needed. The current study will use Single Case Experimental Design to isolate and evaluate the effects of WET in reducing both PTSD symptoms and trauma-related mental contamination among individuals with PTSD resulting from sexual trauma. Aims: Explore whether participants demonstrate reductions in mental contamination and PTSD symptoms in response to 5 sessions of WET. Visual inspection analysis and statistical methods will be used to draw conclusions regarding the effects of the interventions on PTSD symptoms and mental contamination.