Psychopathy has traditionally been characterised as a disorder primarily of personality (particularly affective deficits) and, to a lesser extent, behaviour. Although often used interchangeably, the diagnostic constructs of psychopathy, antisocial personality disorder, and dissocial personality disorder are distinct. There are defferences in diagnostic criteria for psychopathy, antisocial personality disorder, and dissocial personality. Also, consideration should be given to the assessment, prevalence, and implications of psychopathy for violence risk and treatment efficacy. Patients with personality disorder are generally regarded as irritating, attentionseeking, difficult to menage and unlikely to comply with advice or treatment. Suicide attempts and other behaviours by patients previously diagnosed as having personality disorder were comonly regarded as manipulative and under voluntary control rather than the result of illness. Personality disorders are risk and complicating factor for a wide range of mental disorders with great forensic imlications. Forensic psychiatrists have more opportunities than most to contemplate the nature of evil and depravity. They are asked to evaluate individuals accused of committing some of the most horrific acts imaginable. People often assume that serial killers and genocidal leaders are “crazy.” If this were true, psychiatrists might have some expertise to offer in the evaluation of such evil. However, such individuals are rarely psychotic. Some perpetrators of the worst atrocities do not have a diagnosable psychiatric disorder. Part of our fascination with these individuals is their appearance of normality. The Gordian knot of evil cannot be untied by forensic psychiatry.