Post-traumatic stress disorder (PTSD) is a psychiatric disorder whose development is closely related to the experience of a devastating traumatic event or events. Among different biological systems that are disturbed in PTSD, neuroendocrine and immune systems are the most affected. Biomarkers are objective indicators of medical state which can be determined in easy available body fluids and measured accurately and reproducibly. Combat-related PTSD is often associated with psychiatric and somatic comorbidities. Within somatic complications, cardiovascular diseases are the most frequent. Cardiometabolic disorders in PTSD are related to sympathetic over-activation; chronic peripheral, low-grade inflammation and altered HPA axis responses. Dysregulated HPA axis in PTSD is associated with blunted cortisol secretion; low glucocorticoid signalling; impaired negative feedback, leading to the allostatic load and overreactions to moderate stressful stimuli. Review of the biomarkers of the immune system in PTSD and PTSD comorbid with cardiometabolic disorders revealed immunological imbalance and low grade pro-inflammatory state in PTSD, with increased plasma levels of pro-inflammatory cytokines. Since PTSD is a complex and polygenic disorder, associated with different comorbid disorders, impaired stress response and altered immune systems might only describe part of the potential patho-mechanisms underlying PTSD.