1. The epsilon 4 allele of the apolipoprotein E gene increases the risk of late onset familial and sporadic Alzheimer disease. Relation of epsilon 4 allele of the apolipoprotein E gene to various types of dementia and the onset of dementia were analyzed in the present study. 2. The study comprised 139 patients (50 men and 89 women) with dementia, mean age 73.61 years (range 47-98). The diagnosis of dementia was made according to Diagnostic and Statistical Manual of Mental Disorders, and subtypes diagnoses were made according to NINCDS-ADRDA and NINDS-AIREN criteria. Minimental State Examination (MMSE) was used for the screening of dementia. Apolipoprotein E polymorphism was determined by the PCR-RFLP technique-polymerase chain reaction and subsequent digestion with specific restriction endonuclease. For statistical analyses chi-square test and the crude Gart s odds ratio (OR) and 95% confidence intervals (CI) were used. 3. From 139 dementia patients (MMSE < or =24 points) in 61 (45%) Alzheimer disease (AD) was present, in 44 patients (31%) vascular dementia (VD), and in 34 (24%) mixed dementia (MD) were revealed. In comparison with control group the presence of at least one ApoE-varepsilon4 allele was significantly higher only in the group with AD (p < 0.001), (OR=2.76; 95%: 1.42-5.36). The frequency of epsilon4 allele carriers was significantly overrepresented in AD group compared with VD (chi(2)=5.94; p=0.0148). Differences between AD and MD or VD and MD were not confirmed.