Objective: Middle-school-aged children with obsessive-compulsive disorder (OCD) are poised in development between the dependency of elementary school-aged children and growing independence of adolescence. OCD patients of this age group may differ from older ones in the quality of symptoms and level of insight. We report the results of a naturalistic, pilot study of group Cognitive-behavior Therapy (CBT) for school-aged children with OCD with parents involved. The authors predicted symptom improvement and format acceptability. Method: Over a 1.5 year period, 14 children with OCD aged 8-14 years and their parents received 14-week group CBT based on March and Mulle's OCD in Children and Adolescents: A Cognitive-Behavioral Treatment Manual in three consecutive sessions of four to six families. Age of onset averaged 8.7 years, 36% had undergone at least one medication trial, and 36% had previous CBT experience. Results: OCD symptoms measured by the Children's Yale-Brown Obsessive Compulsive Scale improved significantly, both statistically and clinically (25%) from moderate-severe to mild-moderate. Mean Clinical Global Impression of Impairment (NIMH-CGI) Impairment ratings fell from clinical to sub-clinical and CGI Improvement ratings were "much improved". Children's self-reported depression decreased significantly from pre- to post-group. Parent ratings of the negative impact of OCD symptoms on the Children's OCD Impact Scale and of behavior problems on the Child Behavior Checklist each improved significantly. Conclusions: This pilot study, which included a non-selected clinical sample, demonstrates that a manual-based treatment protocol may be effectively adapted for group treatment of different developmental levels and be exported for clinical use. Clinical improvement justifies further investigation in a controlled study.