The discovery of mis-sense mutations linking the presenilin-1 (PS-1) gene on chromosome 14 to Alzheimer's disease (AD) has lead to a thorough investigation of this locus. The PS-1 gene contains a polymorphism creating two alleles. The most common allele, allele 1, has been linked with late-onset AD. Given the clinical and pathological overlaps between AD and dementia with Lewy bodies we genotyped 46 pathologically confirmed cases of dementia with Lewy bodies for the PS-1 polymorphism and compared the allelic frequencies with 87 age-matched control cases and 103 age-matched AD cases. No association between dementia with Lewy bodies and PS-1 allele 1 was found either in the group as a whole, or in the group stratified according to dosage of the epsilon4 allele of the apolipoprotein E gene. We suggest that either the presenilin polymorphism has no effect on dementia with Lewy bodies or that any linkage is precluded by another, more influential, locus.