During a French Peace-Keeping Mission in ex-Yugoslavia in 1996 we were confronted with a peculiar psychic trouble: the agressive behaviour and more precisely the inappropriate use of weapons. Ifs importance is riot a question of quantity but a question of quality because of the threat it represents for the mental health of the combat group. Its clinical expression is: violent alcoholic intoxication serious panic attack with sometimes a hyperexpressivity, or more simply an explosive trouble on the occasion of an interpersonal conflict. On a psychodynamic viewpoint, the agressive behaviour is an acting which expresses the soldiers 'distress. He doesn't want to submit himself to his Ideal's demands that are too difficult for him to fulfil: being an armed soldier is an ideal that would bring him, however, an important narcissic support. On art individual therapeutic viewpoint, the psychiatrist's intervention and his listening enable the soldier. to put into words his act and to express its personal meaning. On a collective viewpoint, the psychiatrist's medico-psychological intervention within the military unit is sometimes necessary after a suicide or a serious agressive behaviour.