U.S. veterans of Iraq and/or Afghanistan (N = 116) completed an Internet survey with questions related to attachment style in intimate relationships, personality factors, and posttraumatic stress disorder (PTSD). Participants completed the PTSD Checklist-Military, Experiences in Close Relationships Scale-Short Form, and the International Personality Item Pool Big Five Short Form Questionnaire. Most participants were male and Caucasian. Hierarchical linear regression analysis results indicated that emotional stability (β = −.46, p < .001) and attachment avoidance (β = .20, p < .05) were associated with PTSD symptom severity (adjusted R2 = .63). An interaction between conscientiousness and attachment anxiety was found (β = −.26, p < .001; ΔR2 = .06), with secure attachment moderating the relationship between conscientiousness and PTSD symptom severity. Results of this study indicate that emotional stability, conscientiousness, and secure relationship attachment styles (low attachment anxiety and avoidance) are important for postcombat mental health.