Background: Thirty-three Japanese children and adolescents diagnosed with an anxiety disorder participated in individual or group Cognitive Behaviour Therapy (CBT) that was modelled after evidence-based intervention programs developed in Western countries. Method: The treatment consisted of: (a) building rapport and education; (b) identifying emotions and recognizing cognitive self-talk; (c) challenging anxious self-talk; (d) developing an anxiety hierarchy and in vivo exposures; and (e) planning for future challenges. Results: Three months following treatment, 20 of the 33 children and adolescents (60.91%) no longer met criteria for their principal anxiety disorders and 16 (48.48%) were free from all anxiety disorders. Self-reported anxiety, depression, and cognitive errors also decreased significantly from pre- to post-treatment and these gains were maintained at 3-month follow-up. For the most part, similar outcomes were found in both the group and individual formats of CBT. Conclusions: This study provides preliminary support for the transportability of CBT in both an individual and group format to Japan.