About half of all persons accused of a criminal offense in Canada are evaluated before trial by a psychiatrist or a multidisciplinary mental health team to determine if they are fit to stand trial. Very few persons, however, are judged as being unable to stand trial. If the accused is determined to be mentally fit, an evaluation may be requested by the court at the pretrial stage to determine if he or she was insane at the time of the alleged offense. Canada has about 13,000 persons, mostly men, in its penitentiaries, and many suffer from major mental disorders. Evidence suggests that mentally disordered individuals are at increased risk to commit violent offenses. Psychologists are conducting research to clarify possible links between mental illness and crime, to identify patients who are at risk for violent behavior, and to understand factors contributing to violent behavior. Psychologists are also playing a leading role in experimental programs designed to identify the mentally disordered person at the time of arrest and provide appropriate care. While psychologists are often not recognized by Canadian criminal courts as evaluators of fitness to stand trial or an accused person's state of mind, they are actively involved as members of multidisciplinary assessment teams. The main contribution of psychologists has been and continues to be the design of structured assessment procedures. Treatment programs for mentally disordered offenders are becoming more structured, systematic, and specific, particularly with respect to behavioral difficulties presented by these offenders. In addition, psychologists are actively involved in evaluating the effectiveness of community treatment programs. 60 references