The first part of the paper reviews Canadian criminal court proceedings. It shows that, in the majority of cases, testimony regarding the diagnosis of psychopathy has been associated with an increase in the severity of dispositions. The second part of the paper summarizes the empirical literature on assessment, prediction, experimental findings, and the treatment of psychopathy. A review of specific court decisions shows that, in many instances, expert testimony was not supported by the empirical evidence available at the time. The author notes that psychopaths can be described as "high-risk, high-need individuals with low responsivity." From a treatment perspective this is the worst possible combination. The diagnosis of psychopathy is often equated with a higher risk of violent recidivism and an inability to benefit from treatment. The portrayal of defendants as psychopaths by expert mental health witnesses may influence judges and be used to justify harsher sanctions. Due to the potential and real consequences for persons who are diagnosed as psychopaths, mental health professionals who agree to conduct assessments and to testify on these findings must meet the highest professional standards. These standards require mental health professionals to have a comprehensive, empirically based, and up-to-date forensic expertise, which should include relevant clinical training. 39 notes and 147 references