Background: Pharmacotherapy is considered an evidenced-based treatment for anxious youth. There is a need to better understand the relation between medication adherence and child outcomes. Objective: This study prospectively examined: (1) baseline predictors of adherence and (2) the relation between medication adherence and clinical outcomes in children and adolescents with anxiety disorders. Method: Participants were 349 youth randomized to sertraline, pill placebo, or sertraline plus cognitive behavioral therapy in the Child/Adolescent Anxiety Multimodal Study and followed over 12 weeks. The measure of pharmacotherapy adherence used was pharmacotherapist (PT) ratings of adherence at each session. Four domains of baseline predictors were examined (demographics, child clinical variables, family/parent variables, and treatment variables). Results: Multiple regression analyses revealed few significant predictors of adherence. The most robust predictors of greater adherence were living with two parents and parents' positive expectations that medication would lead to better outcomes. PTs ratings of higher adherence predicted higher global functioning at post treatment and treatment responder status. Conclusions: In order to increase adherence, improving expectations and instilling hope for positive outcomes and problem solving ways to overcome pragmatic barriers associated with single parent families is recommended.