Telomere length has been suggested to be a cellular marker for age-related diseases as well as psychosocial stress. The present study investigated whether telomere length is associated with post-traumatic stress disorder (PTSD) among veterans exposed to combat trauma in the Vietnam War. The potentially associated factors on cellular aging were considered. Korean male veterans with (n = 122) and without (n = 120) PTSD were included and leukocyte telomere length was measured with a quantitative PCR-based technique. As a whole, no significant difference in telomere length was found between PTSD and non-PTSD groups. In linear regression analysis stratified by trauma levels, among veterans exposed to severe combat (n = 45), PTSD status (B = -1.176, t = -2.259, p = 0.029), antidepressant use (B = 0.168, t = 2.528, p = 0.015), and education level (B = 0.019, t = 2.369, p = 0.023) affected telomere length. However, among veterans with light-to-moderate combat exposure (n = 197), only age (B = -0.007, t = -2.434, p = 0.016) and education level (B = 0.010, t = 2.295, p = 0.023) were associated with telomere length. In the Post-hoc analysis, antidepressant use was associated with longer telomere length in subjects exposed to severe combat. Our exploratory results suggest that PTSD status in combination with severe trauma may be associated with accelerated telomere shortening, and that antidepressant use may have a protective effect on telomere dynamics.