Social anxiety disorder, whose onset peaks in adolescence, is associated with significant impairment. Despite the availability of effective treatments, few affected youth receive services. Transporting interventions into schools may circumvent barriers to treatment. The efficacy of a school-based intervention for social anxiety disorder was examined in a randomized wait-list control trial of 35 adolescents (26 females). Independent evaluators, blind to treatment condition, evaluated participants at preintervention, postintervention, and 9 months later. Adolescents in the intervention group demonstrated significantly greater reductions than controls in social anxiety and avoidance, as well as significantly improved overall functioning. In addition, 67% of treated subjects, compared to 6% of wait-list participants, no longer met criteria for social phobia following treatment. Findings support the possible efficacy of school-based intervention for facilitating access to treatment for socially anxious adolescents.