Examine the association of multimorbidity and psychosocial functioning with posttraumatic stress disorder (PTSD) symptom severity reported among post-9/11 veterans. This was a secondary analysis of survey data collected from a national sample of post-9/11 veterans with at least 3 years of Department of Veterans Affairs care, stratified by comorbidity trajectory and sex (N = 1,989). Comorbidity trajectories were derived by latent class analysis to develop probabilistic combinations of physical and mental health conditions in a previous effort (Pugh et al., 2016). In this study, linear models analyzed symptom severity reported on the PTSD Checklist for the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition by psychosocial factors (i.e., resilience, self-efficacy, and postdeployment social support) while controlling for sociodemographic characteristics and deployment experiences. Veterans in the mental health, pain, and polytrauma clinical triad comorbidity trajectories reported more severe PTSD symptoms than the healthy comorbidity trajectory (p < .01). All psychosocial factors were significantly associated with PTSD symptom severity, accounting for nearly 43% of variability in follow-up analyses. Confidence in self-efficacy demonstrated the strongest association among them (p < .01). Veterans experiencing multimorbidity, particularly mental health distress, reported greater PTSD symptom severity after controlling for psychosocial factors, sociodemographics, and deployment experiences. The salience of psychosocial factors in reported PTSD symptom severity underscores resilience, self-efficacy and social support as potential facilitators of functional reintegration following military service. Our analyses underscore the need to address the systemic barriers in health care access and delivery for minority patient populations in future investigations. (PsycInfo Database Record (c) 2022 APA, all rights reserved).