The article analyses Attention Deficit Hyperactivity Disorder (ADHD), which is one of the most widespread childhood disorders. In Poland about 3-5% of children have clinical ADHD, and 10 -15% of children's population can be characterized by traits of hyperactivity observed in behavior. ADHD manifests as the long-standing, pervasive and developmentally extreme difficulties in hyperactivity (motoric activity), impulsivity and inattention. The origin of ADHD is substantially the result of genetic factors. Psychological mechanisms of ADHD described by Barkley (1997) refer to deficit of inhibition, which is more severe in hyperactive children. The relationship between ADHD and ODD (oppositional deviant disorder) and CD (conduct disorder) is not clear. Some research indicates that 35-60% of ADHD children manifest ODD disorder, and 14% of children present CD problems. Children with ADHD and comorbidity of ODD, CD seemed to be at high risk for significant impairments in social and educational functioning.