The article presents a definition of Post-Traumatic Stress Disorder (PTSD) in descriptive terms according to the DSM IV, from a psychobiological perspective and particularly according to the cognitive-behavioural model. It’s pointed out the importance of extending the trauma’s definition as compared with that presented in the DSM, considering traumatic not only the events that entail a threat to the life or to the physical integrity, but also those perceived in this way by the individual for particular characteristics, such as the negative valence, the unpredictability and the not controllability. These characteristics together with different factors of vulnerability and of risk join the exordium, development, maintenance and severity of the disorder, and it’s important to know them to realize effective interventions in the single case. Afterwards the PTSD’s treatment is considered, particularly the guide lines, the cognitive-behavioural therapy – of which the main components are presented: exposure, cognitive restructuring, prevention of relapses – and other types of cognitive-behavioural interventions, such as the Imagery Rehearsal Therapy and  the Stress Inoculation Training.