Traumatic brain injury (TBI) is a leading cause of disability worldwide. One commonly overlooked effect of TBI is the disruption of the brain-gut axis, leading to gastrointestinal dysfunction. The brain-gut axis consists of the cortical areas of the insular cortex, cingulate, and hypothalamus that have bidirectional communication with the visceral enteric nervous system through afferent and efferent projections into the pontine vagal complex and nucleus tractus solitarius. Communication with the brain also occurs through messenger signals from the gut's microbiota, involving gut peptides, cytokines, and lipopolysaccharides. Disruption of the brain-gut axis from TBI can lead to a chronic, inflammatory, vicious sequela, involving both the brain and the gastrointestinal system, with both neuroregulatory and neuroimmunological loops.