Abstract: Background: Mild traumatic brain injury (mTBI) and impulsivity are risk factors for suicidality. Impulsivity is frequently associated with TBI. Our laboratory recently demonstrated that impulsivity mediates the relationship between TBI and suicidality. The neural mechanisms underlying this relationship remain unknown, however. The medial orbitofrontal cortex (mOFC), involved in impulse control, is vulnerable in TBI. This study investigates mOFC volume differences between Veterans with mTBI and controls to understand its role in suicidality. Methods: Our analysis investigated structural differences in mOFC volumes between Veterans with mTBI (n=43) and Veteran controls (n=8). We processed structural MPRAGE MRI data using FreeSurfer. We reviewed medical charts to identify which Veterans with mTBI had a history of suicidal ideation (SI n=28, no SI n=15). Effect sizes were calculated using Cohen’s d. T-tests and linear regression models were performed. Results: Veterans with mTBI showed a significant reduction in right mOFC volume compared to controls (t=2.59, p=0.026), with a large effect size (Cohen’s d=0.93, 95% CI [0.13, 1.72]). When Veterans with mTBI were categorized by suicidality, linear regression analysis revealed SI was significantly associated with reduced right mOFC volume compared to controls (B=-629.7, SE=241.95, p=.013). Veterans with mTBI without SI did not differ from controls (B=-441.6, SE=259.9, p=.098). No relationships were observed between SI and left mOFC. Conclusions: Our preliminary study reveals a significant reduction in right mOFC volume among Veterans with mTBI and SI. This suggests a link between mTBI, SI, and right mOFC structure. We hypothesize that reduced right mOFC volume may contribute to impulsivity and suicide risk.