The variety of assessment and treatment methods applied to sex offenders result in confusion and misunderstanding in the courtroom, as judges and lawyers try to discern the validity of expert testimony from psychologists and psychiatrists. These professionals describe the new assessment and treatment methods that could be applied to the offender. They also describe how the offender's approach to treatment should be evaluated. A 1981 survey of 57 North American treatment programs for sex offenders revealed that five distinct treatment approaches were being used: group, behavioral, self-help, dynamic (intrapsychic), and drug therapy. Group therapy is cost-efficient and permits offenders to treat one another, but it depends on the validity of offenders' statements, which may be doubtful within the prison setting. Behavioral treatment can be precisely defined and evaluated, but it has a potential for ethical abuse. Self-help treatment is the most cost-efficient approach and deserves attention, although the assessment of treatment outcome is difficult. Dynamic treatment draws on an extensive body of psychoanalytic literature, but it is not cost-effective and its success is based on the opinion of the therapist. Drug treatment is cost-efficient and has a rapid effect, but its effectiveness is easily reversed and it entails frequent complications. Each treatment approach differs in its theoretical basis, underlying goals, and methods. Six criteria by which the court should be guided in judging the validity of expert witnesses' opinions are listed. A table and 18 references are included.