INTRODUCTION: Post-traumatic stress disorder (PTSD) is associated with an increased risk of cardiovascular and metabolic diseases and physical inactivity. Cardiorespiratory fitness (CRF), which is modifiable by physical activity, is a strong independent predictor of cardiometabolic health. However, the relationship between CRF and cardiometabolic health in veterans with PTSD is unknown. Thus, this study aimed to explore the cross-sectional relationships among CRF, indices of cardiometabolic health (ie, HbA1c, blood lipids, blood pressure, waist-hip ratio, and body mass index), and PTSD severity in veterans with PTSD. MATERIALS AND METHODS: This study was approved by the local Institutional Review Board. All participants were informed of the study risks and provided consent prior to participation. Participants (n = 13) completed a cardiopulmonary exercise test, a fasting blood draw, and the Clinician Administered PTSD Scale. Correlations between CRF and cardiometabolic health were examined with Spearman's rank correlations, and differences in PTSD symptom severity were explored as a function of CRF (ie, low-to-moderate vs. high CRF), using multiple linear regression. RESULTS: Peak oxygen uptake ($\dot{\mathrm{V}}$O2peak) was correlated with high-density lipoproteins rho = 0.60, P = 0.04 and diastolic blood pressure rho = -0.56, P = 0.05. Ventilatory threshold was correlated with HbA1c rho = -0.61, P = 0.03 and diastolic blood pressure rho = -0.56, P = 0.05. Higher CRF was associated with lower total PTSD severity standardized β = -0.84, P = 0.01, adjusted R2 = 0.47, total Cluster C symptoms (avoidance/numbing) β = -0.71, P = 0.02, adjusted R2 = 0.49, and total Cluster D symptoms (hyperarousal) β = -0.89, P = 0.01, adjusted R2 = 0.41, while adjusting for age and smoking status. CONCLUSIONS: These preliminary findings suggest that CRF and by proxy physical activity may be important factors in understanding the increased risk of cardiovascular and metabolic disease associated with PTSD.