||How to best treat individuals who commit child sex offenses is a perennial concern. Many of these perpetrators are adolescents. In order for mental health professionals to adequately address this group's unique treatment needs, further research is necessary. The present research addressed the assessment of sexual interest (which may play an integral role in potential for sexual reoffending) in a sample of adolescents at high risk for sexual reoffending. The project compared results from an unobtrusive method of assessing sexual interest (a viewing time measure) to both a physiologically-based method (a penile plethysmography [PPG] measure), and an actuarially-based assessment of pedophilic interest. Results provided evidence for some overlap between PPG and viewing time assessments, although other evidence suggested that whether or not PPG data are ipsatized may impact the relationship of the data with other assessment modalities. Of particular relevance for clinical assessment, results also suggested that the actuarially-based assessment may have limited utility with adolescents. There has also been a dramatic increase in treatment programs for adolescents who have committed sex offenses. Despite this increase, treatment dropout rates are often quite high, and more treatment outcome research is needed. To that end, the present study also explored treatment trajectories and outcome, by examining the relationship between pretreatment variables, psychological distress during treatment, and treatment completion, as well as posttreatment outcomes including sexual reoffending. In a second sample of adolescents in residential treatment for sexual offending, there was no evidence that adolescents who failed to complete treatment, or who had sexual or nonsexual behavior problems following treatment, differed from other adolescents in their trajectories of self-reported distress during treatment. Two trends emerged, however: adolescents who first sexually offended at older ages were slightly less likely to have negative treatment outcomes, whereas adolescents with diagnosed anxiety disorders were more likely to have negative treatment outcomes. Additionally, adolescents with previous academic problems or histories of committing nonsexual crimes experienced different trajectories of self-reported distress than other adolescents, although these trajectories were unrelated to posttreatment outcomes. Implications for research and treatment are discussed.