Objective: Meta-analytic studies have not confirmed that involving parents in cognitive behavior therapy (CBT) for anxious children is therapeutically beneficial. There is also great heterogeneity in the type of parental involvement included. We investigated parental involvement focused on contingency management (CM) and transfer of control (TC) as a potential outcome moderator using a meta-analysis with individual patient data. Method: Investigators of randomized controlled trials (RCTs) of CBT for anxious children, identified systematically, were invited to submit their data. Conditions in each RCT were coded based on type of parental involvement in CBT (i.e., low involvement, active involvement without emphasis on CM or TC, active involvement with emphasis on CM or TC). Treatment outcomes were compared using a 1-stage meta-analysis. Results: All cases involved in active treatment (894 of 1,618) were included for subgroup analyses. Across all CBT groups, means of clinical severity, anxiety, and internalizing symptoms significantly decreased posttreatment and were comparable across groups. The group without emphasis on CM or TC showed a higher proportion with posttreatment anxiety diagnoses than the low-involvement group. Between posttreatment and 1-year follow-up, the proportion with anxiety diagnoses significantly decreased in CBT with active parental involvement with emphasis on CM or TC, whereas treatment gains were merely maintained in the other 2 groups. Conclusions: CBT for anxious children is an effective treatment with or without active parental involvement. However, CBT with active parental involvement emphasizing CM or TC may support long-term maintenance of treatment gains. Results should be replicated as additional RCTs are published.