Background: Cognitive-behavioral therapy with exposure and response prevention (ERP) is an effective treatment for pediatric OCD; however, up to 30 % of children are treatment non-responders and as many as 40% are partial responders. Although poor treatment adherence has been linked to attenuated response in adults with OCD, little research has examined treatment adherence in pediatric OCD. Objective: This study aimed to identify predictors of within-session treatment adherence in pediatric OCD. Method: Independent raters coded 20 audiotaped psychotherapy sessions to assess for in-session adherence to ERP across three separate constructs: willingness to engage in exposure, response prevention, and within-session habituation. A number of baseline predictors were examined in relation to overall in-session adherence, including obsessive-compulsive symptom severity, family accommodation, and externalizing behavior. Results: Higher levels of family accommodation and obsessive-compulsive symptom severity, but not externalizing behavior, were directly linked to poor in-session adherence, and the child's willingness to participate in exposure drove these relationships. Mediational analyses suggested that obsessive-compulsive symptom severity mediated the relationship between family accommodation and in-session adherence to ERP. Conclusions: Findings are preliminary but suggest that targeting family accommodation could increase compliance with exposure tasks, thus improving treatment outcome.