Increasing evidence comes from epidemiological and neuroscientific studies that some forms of violence fall into the domain of psychiatric clinicians and researchers. Epidemiological studies find increased risks of violent behavior among people who are mentally ill, and increased mental illness among people who are violent. Substance abuse, antisocial and borderline personality disorders, conduct disorder, attention-deficit hyperactivity disorder, schizophrenia, mood disorders, anxiety disorders, mental retardation, and organic mental disorders have all have been linked with an increase in violent behavior. Biological studies have identified abnormalities in neurotransmitter systems that are associated with impulsive aggression, a pivotal aspect of some forms of violent behavior. The social and criminal aspects of violence cannot be minimized, but mental health professionals have an important role in research and treatment.