Special Operations Forces (SOF) Soldiers sustain frequent, low-level, occupational blast and mild traumatic brain injury (mTBI). These occupational blast exposures are encountered predominantly in training and do not cause mTBI symptoms. However, the cumulative impact of blast exposure on long-term neurological health is poorly understood. The purpose of this study was to investigate the effect of occupational blast exposure and the interaction effect of mTBI on brain structural changes in SOF Soldiers. Participants (n = 88) underwent neuroimaging assessments including high resolution T1-weighted magnetization-prepared rapid gradient echo (MPRAGE; TR/TE/TI = 2300ms/2.98ms/900ms; slice thickness = 1mm; FoV = 256mm x 256 mm) and T2-weighted MRI sequences (TR/TE = 3200/400ms; slice thickness = 1mm; FoV = 256mm x 256 mm) at two visits Time between visits ranged between participants from 13 to 131 months. Cortical reconstruction and volumetric segmentation were performed with the FreeSurfer image analysis suite (7.2.0). Outcome measures were gross neurostructural changes to cortical volumes at each lobe, the ventricles, and the cerebellum. Months of blast exposure between visits was used to predict change in brain structural outcomes between visits using general linear models. Post hoc subgroup analyses and interactions were assessed. Greater occupational blast exposure predicted increased lateral ventricular volume (F1,86 = 5.45; p = 0.022), left frontal lobe gray matter volume (F1,86 = 4.06; p = 0.047), right parietal lobe gray matter volume (F1,86 = 4.15; p = 0.045), and decreased cerebellum gray matter volume (F1,86 = 5.70; p = 0.019). Although mTBI did not moderate these relationships, subgroup analyses suggest that structural brain changes attributed to blast exposure might be exacerbated by mTBI sustained between visits. Increased lateral ventricle size is typically associated with pathological aging and more severe brain injury. Without concomitant white matter changes, ventricular dilation could indicate decreased cerebrospinal fluid absorption (CSF). This could be caused by glymphatic system dysfunction, which may imply brain waste clearance deficiencies. The cerebellum may be at an increased vulnerability to blast injury. The cerebellum’s location at the skull base and the microvasculature layering Purkinje cells in the cerebellar cortex may contribute to greater susceptibility. Cerebellum gray matter loss may have clinical consequences including dizziness, balance, and coordination issues that warrant further study. Our findings at the left frontal lobe and right parietal lobe were surprising. Given the specific involvement of the right parietal lobe in spatial processing, visuospatial skills, and proprioception, along with the left frontal lobe's role in logical thinking, particularly language processing, production, and word selection, it is possible that these changes could be positive adaptions to specific SOF demands. Specific neurostructural changes are associated with chronic exposure to occupational blast and highlight the potential influence of mTBI in intensifying blast-related changes. Identifying regional brain changes related to blast exposure and mTBI a key step toward informing safe occupational blast exposure doses and developing targeted interventions to preserve Soldier health and readiness.