Adolescents who have sexually offended have unique treatment needs. For mental health professionals to adequately address these unique needs, further research is necessary. To that end, we explored the assessment of sexual interest (which may play an integral role in understanding potential for sexual reoffending) in a sample of 103 male adolescents who have sexually offended. We compared results from a physiological assessment (MONARCH 21 penile plethysmography [PPG]) and an actuarial assessment (Screening Scale for Pedophilic Interest [SSPI]), plus data from an unobstrusive assessment (Affinity, a viewing time measure) in a smaller subsample of 16 male adolescents. One finding that has particular relevance for clinical assessment is that the SSPI may have limited utility with adolescents. We also found evidence for some overlap between data from PPG and viewing time assessments, although whether or not PPG data are ipsatized may affect relationships with other assessment modalities.