Forensic services have shifted their focus to the importance of forensic practice becoming more trauma informed. Trauma exposure is pervasive in forensic mental health populations and has been found to negatively impact the course of severe mental illness (SMI) and increase risk of violence. This study aimed to explore the trauma histories of adult male inpatients in a medium-secure psychiatric hospital, and examine childhood and adulthood trauma as predictors of diagnoses, self-harm, suicidality, hospital re-admissions, substance use, and nature of offense. The case files of 85 male patients in a medium secure unit in the UK were reviewed. Eighty-seven percent of patients had a schizophrenia diagnosis and 86% had extensive trauma histories, the most common trauma type being physical violence in childhood (44.7%). One patient had a PTSD diagnosis. Logistic regressions demonstrated that cumulative childhood and adulthood trauma significantly increased the odds of self-harm. Cumulative childhood trauma exposure was found to decrease the likelihood of having a schizophrenia diagnosis. There is a serious under-recognition of the extent and consequences of trauma exposure; trauma histories are likely greater than the findings of this study and existing literature suggests. Implications for clinical practice, trauma-informed care (TiC), and future research are proposed.