Anxiety interventions involving social skills training and CBT for youth with ASD have shown promise, but few studies have examined the effects on social functioning or the maintenance of treatment gains. This study evaluated change in social skills during a randomized controlled trial of CBT and during the 1-year follow-up for 25 adolescents with ASD and anxiety. We examined the effect of pretreatment social anxiety and loneliness on treatment response. Social impairment improved during treatment and continued to improve through the 3-month follow-up. Although adolescents with higher social anxiety had greater pretreatment social impairment, they showed steeper improvement in social skills during treatment. Loneliness was not a significant predictor of change during treatment. CBT targeting social skills and anxiety can lead to long-term improvements in social functioning.