Ten asymptomatic individuals at risk for Huntington's disease (HD) were determined by the use of linked DNA probes to have a high (HD+ group) or low (HD- group) probability of having inherited the mutant gene. Neuropsychological examination, performed without knowledge of DNA results, revealed impairments in five of seven subjects in the HD+ group. Abnormalities were related to visuospatial abilities or to functions associated with the frontal lobes. All three subjects in the HD- group showed no neuropsychological impairment. Statistical analyses confirmed differences between the HD+ and HD- groups. Affected parents of subjects were at least 12 years older at symptom onset. These results demonstrate that clear neuropsychological impairment may be present in HD even when overt signs and symptoms are not expected for a number of years.