The bulk of the American legal system is based on the moral accountability of individuals, regardless of prior experience, with the exception of the insanity defense. The self-defense laws in many States contain the germ of an alternative perspective. By arguing, as does the Colorado law, that a judgment of self- defense hinges upon understanding the specific reasonableness of an individual's perception of extreme threat based upon that individual's experience, the door opens to a developmental perspective. The best approach involves three steps. First, it documents the specific experiences of the youth involved in lethal violence or other forms of severe aggression, assessing that experience for the joint occurrence of family violence, community violence, and direct experience of traumatic victimization; second, it assesses the situation in which the extreme violence occurred in terms of threatening behavior by the victim, similarity of the situation to prior situations in which the perpetrator was the victim of traumatic victimization, and contextual factors of the parties that would be likely to evoke expectations of attack and legitimize aggressive responses; and third, it assesses the perpetrator's need for rehabilitation experiences that could reduce both hyper-vigilance and legitimization of pre-emptive assault; this is the basis for reducing future risk to the community and the juvenile. These three principles form the basis for a developmentally appropriate forensic approach to youth violence. 53 notes and 1 figure