Post-traumatic stress disorder (PTSD) experienced by children can have a large impact on the wider family. The National Institute for Health and Care Excellence (NICE, 2018) recommend that parents are involved in their child’s PTSD treatment. Studies have found that parents themselves also report high levels of PTSD and other mental health symptoms but few have explored whether these symptoms reduce following their child receiving trauma-focused CBT. In this study, parents (N=29) whose children (ages 8-17 years) were randomly assigned to either 10 sessions of Cognitive Therapy for PTSD (CT-PTSD) or a wait-list control condition (WL) completed the Post Traumatic Stress Diagnostic Scale (PDS), the Patient Health Questionnaire (PHQ-9; to measure depression), the Generalised Anxiety Disorder Questionnaire (GAD-7), and the General Health Questionnaire (GHQ-28; to measure general mental health) for pre-post comparison. Parents whose children were allocated to CT-PTSD reported greater improvements on self-report PTSD, depression, anxiety and general mental health, relative to the WL condition. This trial provides preliminary support for the efficacy of CT-PTSD delivered to children for reducing parent PTSD, depression, anxiety and general mental health symptoms. Replication is needed as well as further exploration of parent factors and frequency of parental involvement required to predict improvements.