Twin and family studies demonstrate that Tourette syndrome (TS) is a genetic disorder. Early segregation analyses of family data were consistent with the hypothesis of autosomal dominant transmission; however, more recent studies suggest that the mode of inheritance is more complex. Current findings suggest that there are genes of major effect with other genes acting as modifiers. Several genome scans have been completed and several regions of interest have been identified that may harbor susceptibility genes for TS. Work is currently underway to replicate and extend these initial results.