The purpose of this single case study was to obtain and discuss data related to the effects of a behavior therapy on an adolescent with generalized social phobia. The treatment was originally designed for administration in group. It consisted of 29 sessions: one group session (educative phase), 12 group sessions dedicated to social skills training, and 16 individual sessions in which the subject received in-vivo exposure. Assessments were made before and after treatment and after a 1-year follow-up. Results show a strong decrease in social anxiety measures at post-test and the long-lasting effects of the treatment.