This study evaluates the effectiveness of a group therapy for juvenile sex offenders. A quasi experimental pre-test/post-test research design including a comparison group has been conducted. The subjects of the control group (n = 22) received traditional services from a Quebec Youth Center. The subjects of the experimental group (n = 29) participated in a 22 weeks group specialized treatment and also received services from the Youth Centers. All of the participants completed a semi-structured interview and 8 questionnaires of the self-assessment type whose items were directly related to the treatment objectives. A first series of analyses aiming to explore the differences between the two groups has been conducted. It shows that the two groups are similar on all but 4 of the 33 dependent variables. A series of paired t-tests shows that the control group obtain significant ameliorations on 3 variables and the experimental group does so on 20 variables between the two measures. However, repeated measures analyses of variances have showed than the experimental group did no better than the control group on the majority of the tested variables. Hypothesis concerning the therapy itself, the subjects and the design of the study are discussed in regard of the results of the evaluation.