Abstract: Objective: Age-related abnormalities in caudate volumes have been reported to differ across the periods of childhood and puberty in children with ADHD. This study assessed caudate volumetric abnormalities across two narrow age clusters within the childhood period.Method: Three-dimensional manual tracings of the head and body of the caudate nucleus and of the cerebrum were acquired from 26 medication-naïve boys with a diagnosis of ADHD (ages 5.9–10.8 years), and 24 age-matched normal controls.Results: Boys with ADHD had smaller total caudate volumes relative to controls, F(1,48)=4.29, p=0.04. Adjustment of caudate volumes with respect to age demonstrated that this group difference was driven solely by participants in the 5.9–7.3 year range, F(1, 46)=5.64, p=0.022, with an effect size of d=0.69. No Group effect was found in older participants, F(1, 46)=0.82, p=0.37.Conclusions: These novel findings suggest a different pattern of caudate volume abnormalities across narrow age clusters prior to puberty in boys with ADHD. Anatomical differences in brain structures related to ADHD in prepubertal children should be evaluated with respect to the changing developmental trajectory of brain regions within this period of rapid brain growth.