Pathologic aggression can be evaluated in terms of its psychosocial provocations, but it also must be recognized as a physiologically generated behavior and that disruptions of those controlling physiologic mechanisms can lead to pathologic states of aggression. Laboratory and clinical evidence indicates that the phylogenetically older limbic system is the anatomic core and that serotonin is the major neurotransmitter linked to that behavior. Hormonal factors influence aggression but are, to a large extent, altered by the aggressive acts themselves. There are a number of recognizable clinical syndromes which, by producing abnormal activity in limbic structures, by interfering with higher cortical control, or by causing neuroendocrine dysfunction, lead to states of pathologic aggression.