Alzheimer's disease is a genetically heterogeneous disorder of CNS. The presence of APOE-epsilon 4 allele is known to increase the risk of early and late onset sporadic and late onset familial forms of AD. In various Western European countries, USA, Canada, Japan and Australia the allelic frequency ranges between 0.1-0.18 in controls, and between 0.24-0.52 in AD patients. In the present study on Polish population, we analyzed the frequency of APOE-epsilon 4 allele in persons with Alzheimer's disease (AD). APOE genotypes were determined in 30 mild to moderate AD (83%) and mixed dementia (MIX, 17%), as well as in 11 nondemented first-degree relatives of AD (NDR), recruited from AD patient registry in Warsaw. Among the AD and MIX patients the APOE-epsilon 4, epsilon 3, epsilon 2 allele frequency was 0.333, 0.65 and 0.017 respectively.