Autonomous hyporesponsiveness in children appears to be an indicator of a greater future likelihood of antisocial behavior. Since externalizing disorders are suggested to implicate a risk of antisocial behavior in later life, psychophysiological measurements were assessed commonly used in the realm of antisocial behavior.Arousal measures and electrodermal responses to orienting and startling stimuli were assessed in 8-13 year old boys diagnosed with attention deficit/hyperactivity disorder (ADHD), conduct disorder (CD), the comorbid condition of ADHD+CD, and in controls. The eyeblink response to startling stimuli was also recorded.Children with CD and ADHD+CD showed decreased electrodermal responses and accelerated habituation in all paradigms compared to children with ADHD alone and controls.CD boys with and without ADHD showed a widely analogous response pattern which is highly similar to that found in antisocial adults. Data suggest that it is CD that sharply rises the risk of unfavorable, antisocial development, whether it occurs alone or comorbid with ADHD.