We investigated 13 patients with Huntington's disease and assessed gait by filming and by gait analyzer before and after increasing haloperidol dosage, until chorea was suppressed or side effects intervened. The severity of chorea and ataxia was scored blindly from videotapes. Gaits were abnormal in 12 of 13 patients and 5 of 6 patients who had symptoms for less than 5 years. Clinical characteristics included wide-based station, lateral swaying, spontaneous knee flexion, variable cadence, and parkinsonian features. Biomechanical analysis illustrated that gait characteristics varied in each walk, with a mean decrease in velocity, stride length, and cadence. Haloperidol treatment decreased chorea but did not affect gait patterns. Ataxia occurs early in the disease, has a distinct but variable pattern, is unrelated to chorea, and is not improved by haloperidol.