Abstract Background: Most of the clinical trials involving cognitive-behavioral therapy (CBT) for the treatment of anorexia nervosa (AN) used the individual therapy format, and few have been dedicated to adapting and assessing the effects of the group format. Objectives: To assess the applicability and effects of a group CBT program for Brazilian adolescents with AN. Methods: Open clinical trial with 22 patients with AN divided into an intervention group – IG (n = 11; CBT, psychiatry, nutrition and family psychoeducation-6 months) and a control group – CG (n = 11; psychiatry, nutrition and family psychoeducation-6 months). Data collected at baseline, at the end of groups and six months after the completion were: weight, height, body mass index and Eating Disorder Examination Questionnaire (EDE-Q) used to assess the severity of AN symptoms. Results: Baseline homogeneous groups, with 91% adherence in the IG vs. 54% in the CG (p = 0.05). Participants in both groups regained weight and decreased symptoms of eating disorders at the end of groups. Comparing the EDE-Q scores IG presented a statistically significant difference in the restraint subscale of the EDE-Q between the end-of-group and the follow-up (p = 0.01). Discussion: Group CBT program produced positive effects and was applicable in Brazilian adolescents with AN as an adjuvant to multidisciplinary treatment.