Akinesia and mental decline appear to be more appropriate criteria than hyperkinesia for the evaluation of the stage and progression of Huntington's disease (HD). In order to establish the relationship between motor and cognitive impairment in the disease, 20 non-demented HD patients were compared with 44 control subjects with respect to motor and cognitive performance. HD patients were significantly impaired in almost all cognitive functions in comparison with controls. Reaction time (RT) and movement time (MT) were considerably slower in HD patients when compared with controls and with patients with parkinsonism. Hyperkinesias did not correlate with cognitive impairment, but there was a good correlation between RT, MT and cognitive functions. Therefore, it seems that akinesia evaluated by RT and MT is an important sign in HD and proceeds at the same rate as mental decay.