Mutations of the tau gene in frontotemporal dementia with parkinsonism and genetic association of the tau locus with progressive supranuclear palsy and corticobasal degeneration directly implicate the tau gene in the aetiology of these tauopathies. Three studies have also shown an association of the tau locus with clinically diagnosed Parkinson's disease. Noting the significant incidence of clinical misdiagnosis of Parkinson's disease, we investigated this tau gene association in a series of 157 pathologically confirmed cases of brain stem Lewy body Parkinson's disease by analysing their tau haplotype status. Although H1H1 homozygotes are elevated in the Parkinson's disease cases (63.1%) compared to controls (56.1%) this difference is not significant (P=0.22). These results indicate that any association must either be weak (with an odds ratio of less than 2) or that previous positive associations were due to contamination of clinically diagnosed cases with other diagnostic clinico-pathological entities such as neurofibrillary tangle Parkinson's syndrome.