This is the first study of adolescents suffering from anxiety disorder in Sweden to receive individually tailored internet-based treatment within a child and adolescent psychiatric clinic. The primary aim of this effectiveness study was to examine the effects of tailored internet-based cognitive behaviour therapy for adolescents.11 adolescents, aged 15-19. years, were allocated to treatment after assessment. Screening consisted of online questionnaires followed by a diagnostic face-to-face interview at the clinic. Treatment consisted of individually prescribed cognitive behaviour therapy (CBT) text modules adapted for the age group. Therapist guidance was via an online platform along with telephone support and face-to-face sessions if needed.Statistically significant improvements were found on all dependent measures immediately following treatment for the 8 adolescents who completed treatment. The within-group effect size on the Beck Anxiety Inventory, the primary outcome measure, was d. =. 2.51 at post-treatment and 80 percent (4/5) adolescents no longer met DSM-IV criteria for their primary anxiety disorder as measured by the Anxiety Disorders Interview Schedule for DSM- IV: Child and Parent Versions.Based on the results from this pilot study the tentative conclusion might be that tailored internet delivered CBT could be useful for adolescents with anxiety disorders along with standard treatment delivered in child and adolescent psychiatric clinics.