This chapter deals with complex concepts and issues concerning the relation of attention-deficit hyperactivity disorder (ADHD) to personality disorders and traits. It presents an account of the risk for ASPD and criminality carried by ADHD. Early-onset disruptive behavior disorder (corresponding to the combination of ADHD, oppositional-defiant disorder (ODD), and conduct disorder (CD), or hyperkinetic conduct disorder) carries a sharply increased risk for later ASPD and aggressive criminality. The chapter talks about the ADHD in relation to personality traits, as defined by the Big Five and Cloninger's temperament and character model. ADHD as a clinical disorder seems to express an extreme end of extroversion or novelty seeking, with possible hampered character development or decreased conscientiousness. The chapter points out the critical role of early regulation and reactivity systems in the development of temperamental or cognitive vulnerability.