Older veterans with posttraumatic stress disorder (PTSD) are at increased risk of obesity and cardiometabolic disease. Physical activity and healthy eating are two behaviors that impact health, functional independence, and disease risk in later life, yet few studies have examined the relationship between PTSD and diet quality. This secondary analysis aimed to: (a) characterize the diet quality of older veterans with PTSD in comparison to U.S. dietary guidelines and (b) explore if participation in a supervised exercise intervention spurred simultaneous changes in dietary behavior. Diet quality was assessed with the Dietary Screener Questionnaire (DSQ), which measures daily intake of fiber, calcium, added sugar, whole grain, dairy, and fruits/vegetables/legumes. The sample included 54 military veterans ≥ 60 years old with PTSD who participated in a randomized controlled pilot trial comparing 12 weeks of supervised exercise (n = 36) to wait-list usual care (n = 18). The DSQ was administered at baseline and 12 weeks. Consumption of added sugar exceeded U.S. dietary guideline recommendations and consumption of whole grains, fruits/vegetables/legumes, fiber, calcium, and dairy fell short. Participation in the supervised exercise intervention was not associated with changes in diet quality. Results revealed that the diet quality of older veterans with PTSD is poor, and while the exercise intervention improved health through exercise, it did not make veterans any more likely to adopt a more healthful diet. Interventions targeting diet, or diet + exercise, are needed to manage the increased risk of obesity and cardiometabolic disease present in older veterans with PTSD.