The purpose of this study was to quantify gait impairments in presymptomatic and symptomatic Huntington's disease (HD) subjects, and examine sensitivity of gait measures. Our sample (n = 65) included presymptomatic mutation carriers (PMC) (n = 15), symptomatic HD subjects (SHD) (n = 30) and healthy controls (n = 20). Participants were requested to walk at their preferred speed on a computerized walkway that recorded spatiotemporal variables. We administered the Unified HD Rating Scale (UHDRS) for PMC and SHD. PMC demonstrated decreased gait velocity (P < 0.01), stride length (P < 0.008), and increased time in double support (P < 0.001); and demonstrated higher variability in stride length (P < 0.01) and step time (P < 0.004) compared with controls. These impairments worsened with increasing disease severity for SHD. Gait impairments were correlated with predicted years to onset in PMC (velocity = -0.65; cadence = -0.70, step time = 0.71) and demonstrated high sensitivity and specificity in distinguishing between controls and mutation carriers. In contrast, UHDRS scores did not reveal impairments in gait and balance. Gait bradykinesia and dynamic balance impairments begin in the presymptomatic stage of HD and continue to worsen in the symptomatic stages. Gait measures are sensitive in differentiating between mutation positive and negative individuals even when impairments were not detected by clinical neurological examination. (c) 2008 Movement Disorder Society.