Delusional misidentification of others occurs when an affected individual believes in changes in the physical and/or psychological make-up of other persons, who usually happen to be in the nearby environment of the affected individual. This conceptualization of inauthenticity of others is often accompanied by the delusional belief that the delusionally misidentified objects are malicious and intend to harm the delusional individual. The anger and fear engendered by the delusionally misidentified object then become the most important factors in motivating aggression toward that object. Understanding the link between delusional misidentification and aggression also requires operational definitions of the basic delusional misidentification syndromes. There are three main delusional misidentification syndromes that involve the misidentification of others in the environment. In Capgras syndrome, the affected person delusionally believes that one or several people in the environment have experienced radical changes in psychological make-up without experiencing changes in physical appearance. A second delusional misidentification syndrome is the Fregoli syndrome, in which the delusionally misidentified object is thought to have a different physical identity but without changes in psychological make-up. In the syndrome of intermetamorphosis, the affected person believes that the misidentified object has a different physical and psychological identity from that of the original object. The level of fear and anger toward the delusionally misidentified object may be a useful indicator in assessing the dangerousness of the delusional person. The subject in the case study, for example, harbored intense anger toward his delusionally misidentified objects exemplified by his threatening putative clones with a knife while in a bar. The subject's delusions, which involved the takeover of the earth by clones and robots, as well as in a conspiracy aimed at replacing the humans on the planet, played a substantial part in the homicide of his stepfather. Important issues that require further study are the possible role of neurological and ecological factors in the genesis of violence in delusional misidentification. There is also a need to study whether specific types of delusional misidentification are more likely than others to lead to homicide or other serious physical harm. 2 tables and 32 references