Tourette's syndrome (TS) is associated with prominent gender differences in clinical expression, tics with a sexual content, and a stabilization or improvement of symptoms after puberty. It is herein hypothesized that some tics can be viewed as inappropriately expressed (normally inhibited) fragments of primitive motor and vocal programs involved in reproductive activity. The brain regions involved in TS (basal ganglia and limbic system) are proposed to be counterparts in humans of those functioning in primitive reproductive behavior whose development and organization are under sex hormone control. It is further hypothesized that sex hormone action is mediated by excitatory neurotransmitter mechanisms such that an excessive trophic effect occurs early in development and a neurotoxic environment emerges later on. The defective gene in TS is hypothesized to influence these developmental processes. This hypothesis has implications for the investigation of the pathogenesis of TS and for experimental therapeutics of the disorder.