Aggressions able to have psychic repercussions may have many sides: war, terrorism, disasters. Psychological or psychiatric reactions show restricted aspects but individual or group reactions must be distinguished between immediate and delayed disorders. About individual reactions, we immediately observe either adapted behaviours (keeping cool, objective risk evaluation, etc.) as pathological behaviours from nevrotic register (anxiety, hysterical and depressive disorders) or psychotic register (confusion, acute, delirium, mania and melancholia disorders). Later, the most common disorders are post-traumatic syndrom and psychosomatic disorders. The immediate collective reactions are also adapted behaviours (well-ordered evacuation, struggle against danger propagation, etc.) and inadapted behaviours (panics "shock-inhibition stupor", centrifugal exodus). Later, we can observe claiming behaviours or "post-disaster mentality". Related to some kind of aggression, specific problems can arise, as "Stockholm syndrom" among hostages. Disorders's ethiopathogeny depends on numerous factors: intensity ans duddenness of aggression, individual predisposition, group psychology. About prevention: before aggression, the prevention requires information and training. Immediatly after, the possibility for the subjects to express what has been lived is really positive. Curative treatments require combination of psychotherapy and chemotherapy.