The neurological, neuropsychological, biochemical, and familial evidence suggesting an organic dysfunctional basis for Gilles de la Tourette's syndrome which interacts with psychological stress factors resulting in manifestations with voluntary and involuntary components is reviewed. In addition, neuropsychological tests results are presented on four cases, two of which are familial ones involving a father and son. The results are discussed in relation to the divergent nature of the limited neuropsychological assessment data to date and the potential utility of additional neuropsychological studies.