Externalizing disorders are the most common and persistent forms of maladjustment in childhood. The aim of this study was to conduct a meta-analysis evaluating the effectiveness of Cognitive Behavioral Therapy (CBT) to reduce externalizing symptoms in two disorders: Attention Deficit Hyperactivity Disorder (ADHD) and Oppositive Defiant Disorder (ODD). The efficacy of CBT to improve social competence and positive parenting and reduce internalizing behaviors, parent stress and maternal depression was also explored. The database PsycInfo, PsycARTICLES, Medline and PubMed were searched to identify relevant studies. Twenty-one trials met the inclusion criteria. Results showed that the biggest improvement, after CBT, was in ODD symptoms (
0.879) followed by parental stress (
0.607), externalizing symptoms (
0.52), parenting skills (
0.381), social competence (
0.390) and ADHD symptoms (
0.343). CBT was also associated with improved attention (
0.378), aggressive behaviors (
0.284), internalizing symptoms (
0.272) and maternal depressive symptoms (
0.231). Overall, CBT is an effective treatment option for externalizing disorders and is also associated with reduced parental distress and maternal depressive symptoms. Multimodal treatments targeting both children and caregivers' symptoms (e.g. maternal depressive symptoms) appear important to produce sustained and generalized benefits.