Little research has been conducted to examine sequential motor functioning of children with Tourette's syndrome (TS) and attention deficit hyperactivity disorder (ADHD). Movement sequencing performance for a group of 12 children with TS and 24 children with ADHD children (12 taking and 12 not taking stimulant medication) and matched control subjects was examined using a serial choice reaction time button-pressing procedure. Aspects of movement preparation and execution were measured for 10 sequential two-way choice points along a response board that extinguished the illuminated target buttons at certain specific times contingent on the previous button press or release. The level of advance information was systematically reduced to provide three levels of reduction of advance information, including no reduction, moderate reduction, and high reduction. Children with TS and ADHD (unmedicated) showed larger increases in down time, reflecting aspects of movement preparation, for the highest level of reduction of advance information than did their respective control groups. These deficits are suggestive of underlying frontostriatal dysfunction. Furthermore, the normalization of performance for children with ADHD taking stimulant medication assists in the confirmation of the validity of such a clinical diagnosis and seems to add to the clinical efficacy of this form of treatment, which has previously been associated with improvements for predominantly attentional and inhibitory symptoms of ADHD.