Recent studies have shown that changes in the basal ganglia circuitry and limbic loops may play an important role both in Tourette syndrome (TS) and attention-deficit-hyperactivity disorder (ADHD). This study aimed to investigate in vivo possible morphological alterations of the amygdala as a key component of the limbic system. Amygdalar and total brain volumes were measured in three-dimensional magnetic resonance imaging data sets of 17 male patients with TS (mean age 11 y 8 mo [SD 2 y]; range 9-16 y) and 17 age-matched comparison children (mean age 12 y 6 mo (SD 2 y 1 mo); range 9-17 y) by volume-of-interest-based volumetry. Eight members of the TS group also fulfilled the diagnostic criteria for ADHD. A significant decrease in the left-hemispheric amygdalar volumes and in the proportions of amygdalar to total brain volumes was observed in members of the TS group compared with the comparison group. Amygdalar volumes did not correlate with tic severity, but with behavioural impairment and especially with symptoms of ADHD. The amygdalar volume reduction might be the pathoanatomical correlate of an impaired input of the amygdala to the striatum and frontal cortex. Future studies should investigate if the involvement of the amygdala is due to TS or rather caused by the genetically-linked most frequent comorbidity ADHD.