Background: Disordered gaming and problem gambling (DG/PG) are associated with a range of functional impairments as well as psychiatric comorbidity. With the proliferation of digital gaming apps aimed at children and adolescents, which involve in-game purchases, there is increasing evidence that DG/PG are on the rise in this age range. The behavior can be detected in youth presenting at school-based health clinics and community psychiatric clinics. Cognitive behavioral therapy (CBT) is one of several recommended treatments for adults, but little evidence is available for the efficacy of this approach in adolescents with DG/PG. Aim: To evaluate the acceptability and feasibility of a CBT-based intervention developed for adolescents with DG/PG, which can be delivered in routine psychiatric care facilities. Methods: Adolescents who were patients at a child and adolescent psychiatry service were screened for DG/PG. Those aged 12-17 years with pronounced symptoms were invited to participate in a 7-week CBT program called Relapse Prevention. Nine adolescents agreed to participate and five consented to repeated assessments of outcome (pre-, post-treatment, and 6-month follow-up). In addition to acceptability and satisfaction with treatment, symptoms of DG were assessed with standardized interview and self-report measures. Results: There were no dropouts from the treatment. Participants who completed treatment and all outcome assessments reported satisfaction with the treatment. The participants showed fewer symptoms of DG after treatment, and the proportion who met criteria for computer game addiction decreased from 56 to 0%. There was no reduction in the number of participants who met criteria for PG. Conclusion: This study provides preliminary evidence for the acceptability and feasibility of a CBT-based intervention for DG/PG in adolescents. Preliminary data suggest that the treatment may be effective for DG but not PG. Further studies are needed to evaluate the efficacy of this approach for both conditions.