Background Adolescents who have displayed harmful sexual behaviour (HSB) are often described as a heterogeneous population, but different offender-, offense-, or victim-based typologies have been proposed. Two common typologies are based on the victim’s age and/or on offender–victim age discrepancies. Methods Using data from a Norwegian clinical sample, we aimed to investigate the characteristics of two subgroups of adolescents: those with younger/child victims (HSB-C) and peer victims (HSB-P). The sample was collected from a public child and adolescent psychiatry outpatient clinic. N = 54 boys, mean age 14.1 (younger age: HSB-C, n = 30, equal age: HSB-P, n = 24). Based on patient records, all patient registries within the sample were reviewed retrospectively. The data were analysed in R with different statistical tests (e.g. N − 1 chi-square test, Fisher’s exact test). Results After adjusting the p values for multiple comparisons, none of the test statistics showed significant results. Based on the magnitude of the effect-size estimates, the following tendencies and potential meaningful differences emerged: more adolescents in the HSB-C group had experienced their own trauma early (V = 0.42), had more than one victim (V = 0.32), and had displayed repeated HSB (V = 0.27), and their caregivers required extensive interventions (V = 0.20). More adolescents in the HSB-P group had cognitive abilities in the normal/high range (V = 0.32), and their caregivers more often had difficulties acknowledging the need for support and treatment (V = 0.20). Conclusions The nonsignificant differences between the subgroups, despite some strong and moderate effects, bring about a discussion on the utility of using “victim age” in combination with the “offender–victim age differences” as the sole classification criterion for adolescents who have displayed HSB. The heterogeneity of the adolescent HSB population and lack of reliable information on more homogenous subgroups dynamics will remain challenges for clinicians and other practitioners needing a broad assessment and intervention focus.

BackgroundAssessing minors with harmful sexual behavior (HSB) is a complex and sensitive task. The AIM3 Assessment Model was developed to assist practitioners with information collection and HSB evaluations.ObjectiveIn this study, we explore the interrater reliability and the practitioners’ experience with the AIM3.Participants and settingThe multidisciplinary sample (n = 56) was recruited in Norway. The participants’ mean age is 43.2 years (SD 9.5). The sample is 79% female and 21% male. Mean years of experience is 17.6 years (SD 9.5).MethodsThe participants used the Norwegian version of the AIM3 to score three case vignettes. A survey containing questions about competence and experience was filled out. We used the intraclass correlation coefficient (ICC) to estimate interrater reliability as well as descriptive statistics to show experience.ResultsThe estimated ICC for overall AIM3 factors is 0.547 (95% CI = 0.471, 0.634); for domain scores, the estimated ICC is 0.697 (95% CI = 0.548, 0.852). Both are in the moderate range. The majority of the participants reported that they will probably use the AIM3 in the future and that their experience with the AIM3 was highly useful with, for example, empirically informed decision-making and for intervention and safety planning.ConclusionThe moderate ICC results and the sample’s generally positive experience with the AIM3 may indicate further usefulness in a Norwegian multidisciplinary setting. We provide recommendations on how the AIM3 and similar HSB assessments can be further evaluated and developed.