We studied postural control, using quantitative moving-platform posturography, in 20 patients with Huntington's Disease (HD) and in 20 age-matched controls. HD patients showed considerably more anterior-posterior sway than normals, even when a correction for chorea was attempted. This increase in sway was especially true when, by eliminating visual and by attenuating proprioceptive cues, patients were forced to rely primarily on vestibular cues for balance. HD patients also showed increased latencies (30-50 ms) but normal amplitude, in response to translational perturbations of the platform. HD patients showed increased amplitude of responses to rotational perturbations of the platform but a normal decrease in response on successive trials. Thus, patients with HD show a consistent pattern of abnormality on posturography suggesting a role for the basal ganglia in a number of aspects of postural control.