Background: Interventions for the treatment of anxiety disorders in children have a growing evidence base. Cognitive-behavioral therapy for the treatment of specific anxiety disorders in children and adolescents, including obsessive-compulsive disorder, is now an established intervention. However, a question remains concerning the benefits of parental involvement in treatment. Some studies report limited or no benefit of including parents in treatment, whereas other studies have indicated additional advantages of parental involvement. Intervention: The present case report describes the treatment of an 11-year-old girl with obsessive-compulsive disorder using cognitive-behavioral therapy derived largely from the treatment approaches outlined in Carr (2006), March and Mulle (1998), and Derisley, Heyman, Robinson, and Turner (2008). The child’s mother attended all sessions and also a one-off parent-only session toward the end of treatment. The report considers the benefits of involving the child’s mother in treatment and possible factors that could suggest parental involvement is indicated in future cases. Outcomes: Both child and mother, and the therapist, believed that parental involvement had been an important and useful element of treatment. Possible reasons for benefits of parental involvement were considered to be high parental anxiety at the outset of treatment, age of the client, and involvement of the parent in obsessions and compulsions.