Abstract: Objective: Post-traumatic stress disorder (PTSD) and hypertension are highly prevalent among Veterans. Cognitive dispersion, indicating within-person variability across neuropsychological measures at one time point, is associated with increased risk of dementia. We examined interactive effects of PTSD symptom severity and hypertension on cognitive dispersion among older Veterans. Methods: We included 128 Vietnam-era Veterans from the Department of Defense-Alzheimer’s Disease Neuroimaging Initiative (DoD-ADNI) with a history of PTSD. Regression models examined interactions between PTSD symptom severity and hypertension on cognitive dispersion (defined as the intraindividual standard deviation across eight cognitive measures) adjusting for demographics and comorbid vascular risk factors. Results: There was an interaction between PTSD symptom severity and hypertension on cognitive dispersion (p = .026) but not on mean cognitive performance (p = .543). Greater PTSD symptom severity was associated with higher cognitive dispersion among those with hypertension (p = .002), but not among those without hypertension (p = .531). Results remained similar after adjusting for mean cognitive performance. Conclusions: Findings suggest, among older Veterans with PTSD, those with both hypertension and more severe PTSD symptoms may be at greater risk for cognitive difficulties. Further, cognitive dispersion may be a useful marker of subtle cognitive difficulties. Future research should examine these associations longitudinally and in a diverse sample.