The goal of this study is twofold: (1) to assess brain anatomical differences between children meeting diagnostic criteria for oppositional defiant disorder (ODD) and healthy controls, and (2) to investigate whether morphological brain characteristics associated with ODD differ in boys and girls. Eight-year-old participants (N = 38) were scanned using magnetic resonance imaging. ODD symptoms were assessed using the Dominic-R interactive. In ODD participants, we observed a significant reduction of gray matter density in the left orbitofrontal cortex--a prefrontal region that plays a pivotal role in emotional self-regulation and impulse control--and, conversely, an increase in the left temporal area--an area that has been associated with aggressive, impulsive, and antisocial personality. Furthermore, ODD boys showed a reduction of both gray matter density in the left orbitofrontal cortex and of white matter density in the left superior frontal area. The structural abnormalities found in the present study, in particular, the correlation between ODD symptoms and reduction of gray matter density in the left orbitofrontal cortex, may present some evidence for the existence of neuropathology associated with ODD symptoms during childhood. Furthermore, our findings indicate morphometric differences between boys and girls with ODD, which may be associated with gender differences in social behavior in children showing ODD symptoms. (Contains 5 tables and 3 figures.)