Individuals with HD who are ambulatory and are either already taking Xenazine or have been newly prescribed the medication will be recruited for this prospective open-label study. A variety of motor assessments will be preformed while subject are taking Xenazine or after a period off of the medications. These tests include: Unified Huntington's Disease Rating Scale (UHDRS) motor section, GAITRite forward walking, Tinetti Mobility Test, Timed Sit-to-Stand Test, Timed Stair Climb Test, Rhomberg test. A subset of subjects will wear an activity monitoring device on the wrist of the non-dominant hand for 5 consecutive days and nights.