Individuals with preexisting psychological difficulties are at risk of further deterioration of their mental well-being during the COVID-19 pandemic. This longitudinal study, conducted during the period between two national lockdowns, aimed to investigate the impact of the COVID-19 pandemic on veterans in the United Kingdom with preexisting mental health difficulties. Treatment-seeking veterans with preexisting mental health difficulties (N = 95) were surveyed in two waves. Wave 1 was conducted at the end of the first lockdown (June 2020-July 2020), and Wave 2 took place during the second lockdown (November 2020).Participants completed measures to assess symptoms of posttraumatic stress disorder (PTSD); common mental health difficulties (CMDs), including anxiety and depression; anger; and alcohol use. Initial analyses revealed no significant changes in symptoms of PTSD, CMDs, anger, or alcohol use between the lockdowns, ps = .247-.986. However, veterans who experienced more COVID-19related stressors were more likely to experience increases in PTSD, odds ratio (OR) = 6.30, p = .002, and CMD symptoms, OR = 4.32, p = .025. Participants 330