Psychological distress is often observed in patients with gastrointestinal illness. To date, there has been limited research conducted to assess the prevalence and impact of post-traumatic stress disorder (PTSD) in gastrointestinal cohorts. The aim of this systematic review is to review the evidence for the prevalence of PTSD in gastrointestinal cohorts versus comparator groups (healthy controls and chronic illness groups), predictive factors associated with the development and management of PTSD and the impact on patient outcomes. Adult studies were identified through systematic searches of eight databases (MEDLINE, Embase, Emcare, PsycINFO, Ovid Nursing, CINAHL, Informit Health Collection, and Cochrane Library) in February 2020. The overall pooled prevalence rate of PTSD in GI cohorts was 36%; however, the prevalence rate in non-veteran-specific gastrointestinal cohorts of 18% across all GI classification groups is likely to be the more representative rate. The non-gastrointestinal chronic illness cohort PTSD prevalence rate was 11%. Predictors identified in the development of post-traumatic stress in gastrointestinal cohorts include: female gender, poor social support, life adversity, subjective pain, and dietary choices. Post-traumatic stress was found to exacerbate gastrointestinal symptoms in a Crohn's Disease sample, whereby disease exacerbation was four times in those who met the criteria for probable PTSD. Post-traumatic stress symptoms affect around one in five individuals (non-veteran status) with a gastrointestinal condition. Further research is needed to understand the psychological and biological mechanisms by which PTSD increases the risk of developing and exacerbating gastrointestinal symptoms.