Three cases of Gilles de la Tourette's syndrome (GTS) who experienced different tic related behaviours in response to both external and internal stimuli are described. Such behaviours might represent sensory tics, reflex motor tics, exaggerated startle responses, or obsessive compulsive behaviours. It is suggested that there is a continuum of stimulus induced behaviours, and that, in some cases, separations into individual descriptive entities may be difficult. There also seems to be a continuum between internal and external phenomena that induce the behaviours. Implications for the relation between GTS and obsessive compulsive disorder are also discussed.