Among 60 patients with Tourette's syndrome (TS), whose mean age was 11.9 years, migraine was prevalent in 26.6%. This figure is substantially greater than that reported for the general population of school-aged children (4.0% to 7.4%) or for two control groups consisting of children with seizure disorders (n = 72) and learning disabilities (n = 62). The prevalence rates for these two control groups were 11.3% and 8.0%, respectively. The hypothesis is offered that the coexistence of TS and migraine in a subgroup of children with TS may reflect a similar abnormality underlying both conditions; specifically, neurohumoral dysfunction involving serotonin metabolism.