Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder which starts in childhood and is characterized by symptoms of attention deficit, hyperactivity and impulsivity. Persistence into adolescence is frequently associated with among other low educational achievement, interpersonal difficulties, anxious and depressive symptoms and sleep problems. Treatment guidelines recommend psychological treatment as part of the treatment plan, however compared to children and adults, there is still a substantial lack of knowledge about appropriate psychological treatment in adolescents. The present study examines a psychological intervention for adolescents with ADHD, cognitive behavior group therapy. The intervention consists of 12 weekly cognitive behavioral therapy sessions addressing core difficulties and concerns of the adolescent population with ADHD. The investigators wish to determine the efficacy of group therapy in adolescents with ADHD who receive medical treatment but still have impairing ADHD symptoms.