Posttraumatic stress disorder (PTSD) is a serious and devastating psychiatric illness that develops after an exposure to a terrifying event. PTSD is associated with a diminished quality of life and considerable emotional suffering in patients and their families, and can be a financial burden to the whole society. PTSD symptoms include preoccupation and re-experiencing of the traumatic event, fear, anxiety, arousal, sleep disturbances, nightmares, emotional numbness, withdrawal, terror, helplessness, horror, irritability and aggression, and the loss of the sense of basic safety. However, not all subjects exposed to a traumatic event will develop PTSD. Brain regions mediate the stress response via specific neurochemical circuitry, but in PTSD the copping mechanisms change from normal reactions to stress into maladaptive responses. The studies of the neurobiology of PTSD, which primarily involves the neuroendocrine dysregulation (of the activity of the hypothalamic-pituitary adrenal axis), dysfunction of the noradrenergic, serotonergic, dopaminergic, GABA-ergic, glutamatergic, and opioidergic neurotransmitter systems, and genetic polymorphisms, might improve the understanding and treatment of PTSD. A complex interaction between trauma and genetic and environmental factors, and early experiences, underlies the development of PTSD. The authors present a review of their own results related to biomarkers in Croatian war veterans with combat related PTSD.