Although they are likely to add their effects, physical and psychic traumata (or traumas) can provoke in different ways the appearance of depressive symptoms sometimes common. Post-traumatic depression, reactional depression, major depressive disorder and post-traumatic stress disorder represent different clinical and nosographic disorders in despite of their occasionally common symptomatic core. Historically, it is interesting to note during the XXth century the true semantic change of the terms of trauma from the somatic field to the psychic sphere. Physical traumatism is often represented by a material shock for the subject and by its organic consequences. It is defined as an event that leaves its mark which itself inflicts and handicaps the vital trajectory of the subject. It primarily comprises brain and rachis injuries, whose evolution is frequently characterized by the occurrence/appearance of a depressive disorder, whose genesis rests on psychological but also neurobiologic and physical arguments. Thus major depressive disorders are often present in the course of various physical traumatisms mainly related to nervous system. In accordance with several studies, the prevalence of major depressive disorders ranges from 25% to 50%. These mood disorders occur in the year which follows the accidental event. Their average time of revelation is estimated at four months and their average duration lies between three and six months. Lastly, although these depressive illnesses present clinical symptoms comparable with those observed in other contexts, some nuances can be raised. Nonetheless, they confine sometimes with true clinical forms depending on the intensity, the form, the circumstances or the consequences of the trauma. Psychic traumatism doesn't have the same profile and rests for much dedicated with the reexperiencing. Thus for some authors, depression illness represents a disorder that occurs after a traumatic event whereas others see a differential diagnosis which exludes or which represents a comorbidity with post-traumatic stress disorder. The review of the literature allows us to emphasize the complexity of the links as well as the clinical and epidemiologic differences between stress disorder and major depressive disorder. From the clinical point of view, the major features of PTSD are articulated around a triad of symptoms. They include the reexperiencing symptoms of the traumatic event such as intrusive memories and recurrent nightmares, the protective reactions such as avoidance of the stimuli associated with the trauma and emotional numbing, and the arousal symptoms such as the startled response and hypervigilance. The complexity of this syndrom is due to the frequent combination of these symptoms with other nonspecific ones. As far as the mood is concerned (the mood symptoms are concerned), the regrouping of some of these symptoms allows the clinician to sometimes releave a depressive symptomatology without being able to assess the DSM diagnosis of major depressive disorder. Epidemiologic studies dealing with the risk of installation of a PTSD after a traumatic event reveal differences in the prevalence depending on the nature of the traumatic events: ranging from 1% in general population to 80% following some situations of extreme and durable psychic suffering. Between both poles, one finds a prevalence ranging between 20 and 50% following other events such as serious accidents, natural disasters or criminal assaults. The clinical features of depressive episodes comorbid or associated with PTSD have some characteristics making it possible to individualize various clinical forms as a function of traumatic event type: asthenic, characterial or with somatic symptoms. According to the majority of authors, the co-occurrence of post-traumatic stress disorder and major depressive disorder is high although differential diagnosis is sometimes difficult. However, conceptual differences remain and two conceptions are distinguished. For some authors, like Bleich and Shalev, there would not be true chronological evolution from PTSD to MDD. Moreover the presence of symptoms considered as pertaining to the mood register within the criteria of PTSD would be clearly predictive of the occurrence and the severity of the diagnosis but not of the chronicity. For others, there would be a continuity between post-traumatic stress disorder and major depressive disorder. It is the case in many studies of veterans but also for civilian traumatic events. It is also the case for the American national study of comorbidity in which Kessler concludes that for 78% of the subjects who present a comorbidity PTSD/MDD (comorbidity raised for 48% of the 5,877 subjects included), the mood disorder is secondary to PTSD. (ABSTRACT TRUNCATED)