The authors evaluated the criteria that are cited in the literature as predictive of homicidal predisposition. They applied three categories of criteria--clinical, developmental, and environmental factors--to a study group of 10 adolescents who had committed homicide, 10 who had threatened or attempted homicide, and 10 hospitalized controls. Their findings did not support the presence of a well-crystallized predisposition for homicidal behavior in this population, but they did show that the adolescents who committed homicide were psychotic-regressive and those who threatened or attempted homicide were organic-impulsive. The study strongly suggests the importance of environmental factors in reinforcing homicidal behavior.