In our cohort of 42 healthy children (HC), 41 ADHD children, and 71 children with TS, we first computed scaling coefficients for the left and right globus pallidus, putamina, caudate nuclei, thalami, amygdalae, and hippocampi. We then independently applied hierarchical clustering to those coefficients that differed significantly (P-value<10−7) between (1) ADHD children and HC, and (2) TS children and ADHD children. The left dendrogram suggested the presence of two groups: one (labeled as HC) consisted of 36 healthy children, and the other (labeled as ADHD children) consisted of the 41 ADHD children and 6 healthy children. The right dendrogram suggested that the brains were clustered into two distinct groups: one labeled TS only comprised of TS children and the other labeled ADHD only consisted of ADHD children. The adjusted misclassification rates (Table 1) were: 11.5% for healthy children and 6.4% for ADHD children; and 0.17% for TS children and 0.5% ADHD children. Therefore, the sensitivity and specificity were: 93.6% and 89.5%, respectively, for classifying a child as an ADHD child; and 99.83% and 99.5%, respectively, for classifying a child as having either ADHD or TS. We plotted the patterns of surface features across the various brain regions that best classified a child. Left: The patterns that discriminated ADHD child from healthy child were localized to: lateral and posterior portions of the right putamen; anterior portions of the left and medial portion of the right globus pallidus; ventral portion of the left caudate; posterior and medial portions of the left thalamus; ventral portion of the left amygdala, and anterior and posterior portions of the right amygdala; and posterior portion of the left hippocampus. In red are regions with local protrusions, and in violet are regions with local indentations in ADHD children compared with the healthy children. Right: The pattern of surface features that discriminated between children with TS or ADHD included: anterior, lateral, and dorsal portions of the left globus pallidus, and dorsal, lateral, and medial portions of the right globus pallidus; ventral portion of the left caudate; dorso-medial portions of the left putamen, and lateral, dorsal, and medial portions of the right putamen; dorsal, posterior, and medial portions of the left thalamus, and posterior portion of the right thalamus; dorsal and posterior portions of the left amygdale, and anterior and posterior portions of the right amygdala; anterior and medial portions of the left hippocampus, and lateral portions of the right hippocampus. Regions in red are local protrusions, and regions in violet are local indentations, in TS children compared with ADHD children. GP, globus pallidus, CN, caudate nucleus; PUT, putamen; TH, thalamus; AMY, amygdala; HC, hippocampus; A: Anterior; P: Posterior.