We assessed 1084 teenagers. In 364 (33.6%) of them Internet-addictive behavior was found. According to results of neuropsychological tests Internet-addictive adolescents compared with healthy adolescents were characterized with flatness of hemi-sphere reciprocity, functional insufficiency of hemi-sphere commissures and sinister anterior lobe – it causes fatiguability, deficit of mental alertness and deficit of regulation of behavior. Virtual environment, in particular, virtual games, stimulate CNS and enhance mental alertness. Longtime warm activity in cyberspace results higher fatiguability, which intensifies Internet addiction. Thus vicious circle of Internet addiction forms. Emotional intellect is significantly lower in Internet-addicts than in healthy adolescents – as a result Internet addicts have problems in identifying emotional state of people, in understanding of relationship and as a result in social adaptation. Internet-addictive adolescents are characterized with high impulsiveness, insufficient mental alertness and behavior and emotional self-control which also results maladjustment. Adolescents with excitable, introversive and asthenic-neurotic personality traits have high risk of Internet addiction. Family education of Internet addicts is characterized with either hyper either hypo protection either ambivalent type. To summarize in Internet addicts functional insufficiency of CNS is the source of personality traits as impulsiveness, excitability, hyperprosexia, deficit of mental alertness and deficit of regulation of behavior and emotions. Disharmonious type of family education results in enchancement of personality traits and maladjustment. Biological basis and disrupted family education complicate forming of emotional intellect which is needed for social adaptation. All these factors result escape of adolescent into virtual environment, in which adaptation is easier.