The authors recommend taking into account risk level, dynamic risk domains, and individual characteristics that may influence whether or not treatment of a sex offender will be successful. It may be that offenders who present different risk for reoffending respond differently to treatment. There is a growing body of research which suggests that treatment is most effective when administered according to the "risk principle." According to this principle the most intensive treatment should be offered to the highest risk offenders, with little to no treatment being provided to low-risk offenders. This principle requires that there be an accurate assessment of the risk for reoffending. Risk can be assessed in a number of ways, including structured actuarial measures and the use of unstructured clinical judgment. The reliability and validity of the most commonly used actuarial risk-assessment instruments have been well established. These instruments measure historical static (unchangeable) variables. Clinical judgments of risk are needed for dynamic factors that are subject to change over time, such as level and type of sexual interests, belief systems, attitudes, self-regulation, and social skills. Individual offender characteristics that are critical in determining progress in treatment are the presence of psychopathy and motivation for treatment. Psychopathy is a condition marked by interpersonal traits, e.g., grandiosity; pathological lying; lack of emotional depth, empathy, guilt, or remorse; and antisocial traits (impulsivity and persistent violation of social norms). Motivation for treatment can be conceptualized in terms of acceptance of accountability for offending, willingness to attend treatment, and a strong desire to adopt behaviors that build constructive, responsible intimate relationships. 124 references