Assessment of the adolescent sex offender requires multiple informants, a sexual developmental history and examination of patterns of child maltreatment, school adjustment, nonsexual delinquent behavior and family and peer influences. The chapter discusses recommended diagnostic and evaluative psychological measures as well as providing a general description of how to approach the adolescent sex offender. A clinical assessment of the youthful sex offender, including psychological testing, can contribute to decision making in at least two key areas. Clinical assessment can inform decisions about the optimal treatment setting and level of restrictiveness necessary to meet the offender’s needs while protecting the safety of the community, based on a comprehensive assessment of risk and dangerousness. It can contribute to treatment planning by allowing the clinician to identify the offender’s strengths and deficits and therapeutic needs. Table, references