OBJECTIVE Behavioral multimodal therapeutic approaches have proven effective in the treatment of conduct disorders. Yet there are hardly any findings regarding the effectiveness of outpatient treatment approaches. This article introduces an intensive behavioral therapeutic program for the reduction of aggressive behaviors (VIA - Verhaltenstherapeutisches Intensivprogramm zur Reduktion von Aggression). VIA combines a intensive outpatient group program for children, aged 8 to 14 years, with accompanying parent training. This study investigates the effectiveness of the VIA approach in reducing aggressive and comorbid symptoms. Furthermore, it pursues the question of the differential therapy effectiveness. METHODS We evaluated the treatment program within the framework of a waitlist-group study design. Pre-post changes and predictors of treatment efficacy were assessed via multivariate analyses of variance and a linear regression model, respectively. RESULTS A group of 36 boys and their caregivers took part in the study. The between-groups comparison revealed a significantly greater reduction of oppositional behavior problems and co-morbid symptoms of ADHD in the intervention group (IG, n = 18) compared to the waitlist group (WG, n = 18). In addition, age and degree of dissocial-aggressive behavioral symptoms were identified as crucial predictors. CONCLUSIONS This study shows that the VIA intensive therapeutic treatment program is effective in reducing aggressive behaviour and comorbid ADHD symptoms in patients with conduct disorder.