Because of the enormous human and financial costs society incurs as a result of sexual crimes, any reduction in the recidivism of sex offenders caused by treatment is very worthwhile. Although treatment can be valuable if this reduction is small, the reduction must nevertheless be real. Real effects are statistically significant differences between treated and untreated subjects in controlled studies. In general, statistical significance is a necessary criterion for clinical and economic significance. In the field of sex offender treatment, it is likely to be a sufficient condition as well. In the view of the authors, the effectiveness of treatment in reducing sex offender recidivism has not yet been scientifically demonstrated. To demonstrate the effectiveness of sex offender treatment, more well-controlled outcome research is required that can be evaluated with meta-analytic techniques.