Abstract: Objective: Adverse childhood experiences (ACEs) are consistently linked with poorer psychosocial and mental health outcomes, including in military veterans. Military veterans are an at-risk group because of the combined risk factors of ACEs and being more likely to experience high stress and trauma in adulthood. This study aimed to report rates of self-reported ACEs in a clinical sample of U.K. military veterans, and to test for associations between high levels of ACEs and psychosocial variables. Method: Participants were a clinical sample of military veterans who were seeking treatment for mental health issues at a U.K. veterans mental health charity. Participants completed surveys relating to their experiences of ACEs and their current mental health and well-being. Associations were tested using regression analyses. Results: A high proportion (35%) reported a high-risk level of 4+ ACEs. Higher ACE scores, and reporting 4+ ACEs were not associated with any specific mental health outcomes, but were associated with having low levels of perceived social support (OR = 0.2000, 95% CI [0.083, 0.482]). Conclusions: Military veterans are at high risk for experiencing multiple ACEs which may leave them more likely to develop to mental health difficulties in adulthood. Additionally, those with high ACEs may require additional help in accessing social support as this is a key risk/protective factor in mental health issues such as posttraumatic stress disorder.