However narrowly defined, mentally disordered offenders (MDOs) are heterogeneous in demographics, diagnoses, offense characteristics, risk, and clinical needs. Treatment planning for MDOs should begin with an assessment of risk of future violent behavior in the community and risk of violence toward self or others inside an institution. Purposes of treatment among MDOs include treatments both to reduce risk of future violence and to alleviate the mental disorder. Relevant outcome measures include criminal and violent behavior, psychiatric symptomatology, admission to correctional or psychiatric facility, and quality of life. Clinical problems include aggression and problems of institutional management, criminal propensity, life skills deficits, substance abuse, active psychotic symptoms, social withdrawal, and depression. Because evidence relating them to risk of future violence is highest for the first 4 problems, it is argued that inpatient treatments should especially target them. Whenever risk levels and legal circumstances permit, community treatment is to be preferred. Sex offenders are discussed as a group for whom specialized services are indicated. Relapse prevention and program development evaluation are recommended methods for guiding treatment planning at both individual and system levels. Obstacles to implementation of empirically based treatments are discussed, as are suggestions for overcoming such obstacles. Finally, promising directions for future research are suggested.