The P3 wave is one cognitive component of event-related potentials (ERP) used to investigate various types of dementia. The aim of this study was to use the odd-ball paradigm to evaluate the P3 in Huntington's Disease (HD) gene carriers who showed no symptoms of chorea, compared to a group of mildly affected HD patients. We selected 14 HD patients and six individuals who, despite testing positive for the HD gene, did not show any clinical evidence of the disease. Thirty-six normal subjects were also selected as controls. Statistical evaluation of N1, P2, N2 and P3 latencies and amplitudes was performed in each group. Both the N2 latency and the P3 latency corrected for age (cP3) were significantly correlated with the duration of illness in pooled symptomatic and presymptomatic gene carriers. However, these latencies did not correlate with any clinical scale or psychometric test, including WAIS subtests. As the individual P3 latency of the majority of HD patients and all presymptomatic gene carriers was distributed within normal confidence intervals, and no correlation existed between ERP parameters and the signs of illness progression, the data appear to provide preliminary evidence against the valence of P3 in detecting the early cognitive impairment of HD.