The authors investigated the efficacy of static versus dynamic approaches to risk assessment and the validity of the Risk Principle through comparing treatment changes made by high- versus lower-risk offenders. The investigations were carried out using a sample of 321 treated sex offenders followed up for an average 10 years postrelease. Risk was assessed using the Static 99, and treatment change was assessed using the Violence Risk ScaleSexual Offender version. Actuarially high-risk/low-change offenders had significantly higher rates of sexual recidivism than similarly high-risk offenders who had demonstrated greater treatment changes. The Static 99 predicted sexual recidivism well among sex offenders with smaller treatment change but demonstrated weaker prediction among offenders with greater treatment change, likely owing, in part, to the static nature of the risk predictors. Implications regarding the dynamic nature of risk and potential utility of incorporating treatment changerelated information into sex offender risk assessments are discussed. (Published Abstract)