Abstract: Subthreshold posttraumatic stress disorder (PTSD) refers to sub-clinical PTSD which may entail functional impairment and distress associated with symptoms of PTSD, without meeting criteria for threshold PTSD. The current study explored the prevalence and mental health associations of subthreshold PTSD in a clinical sample of UK veterans seeking support for mental health difficulties, for whom subthreshold PTSD may be of particular relevance. The sample was drawn from a clinical database of a UK national charity. In total 881 veteran records were extracted which included participants' available demographic data, and PTSD, anxiety, depression and alcohol use measures routinely collected as part of treatment. Overall, those with subthreshold PTSD appeared to have less severe symptoms of PTSD than PTSD. However, only definitions of subthreshold PTSD which required meeting DSM-5 criterion D (negative alterations in mood associated with index trauma) and criterion E (hyperarousal associated with index trauma) were associated with greater symptom severity than those without PTSD. These findings indicate possible clinical utility of a subthreshold definition requiring endorsement of these symptoms in clinical veteran services. Future research might further explore these definitions of subthreshold PTSD and how individuals who meet these criteria might be supported.