Objective: Volumetric differences in the putamen of boys with ADHD combined subtype with psychopathic traits and controls are investigated. Method: The putamen in 24 archival magnetic resonance imaging scans of 12 boys in residential treatment with symptoms of ADHD and psychopathic traits and 12 community control boys are analyzed using Display software. Results: There are no differences found in the total, left, and right putamen volumes across the ADHD or control group. A significant reversal of asymmetry across groups is found; children with ADHD more frequently have a smaller left putamen than right. In contrast, the control group more frequently has a smaller right than left putamen. Conclusion: A reversal of symmetry in the putamen (as found in the caudate) may relate to ADHD symptomology as well as to psychopathic traits. (Contains 1 table and 3 figures.)