This article outlines the parallels between major theories of attention deficit hyperactivity disorder (ADHD) and relevant temperament domains, summarizing recent research from our laboratories on (a) child temperament and (b) adult personality traits related to ADHD symptoms. These data are convergent in suggesting a role of effortful control and regulation in the core symptoms of ADHD. Negative approach and anger is also associated with ADHD, but this may be due to the overlap of ADHD and antisocial behavior. Positive approach may be involved in an alternate pathway to ADHD. The involvement of effortful control is congruent with experimental findings of executive functioning deficits in children with ADHD. We hypothesize that, whereas regulation problems may occur in most children with ADHD, a subgroup also may be characterized by positive approach problems and another subgroup by negative approach problems. We conclude with a theorized multiple process developmental model outlining alternate pathways to ADHD that warrant empirical investigation to better resolve etiological heterogeneity in ADHD.