We examined whether dynamic measures of postural stability differentiated persons with stereotyped movement disorder from persons with dyskinetic movement disorder. Participants from three groups (stereotypy, dyskinesia, control) were given a goal-oriented postural stability task, and performance was measured using a force platform and computerized posturographic techniques. The results showed that both movement disorder groups differed from the control group in the posture task. Further, the stereotypy and dyskinesia groups demonstrated markedly different postural movement profiles. The postural motion of the stereotypy group was characterized by greater amplitude and variability but lower complexity than the dyskinesia group. These results provide support for a motor control model of stereotypy.