We determined the variants of the apolipoprotein E (apo-E) in a sample taken from a castellano-leonesa population with Alzheimer's disease (AD). The prevalence of the allele E-4 is 0.33 in AD and 0.12 in the control group. This results allow us to estimate that the risk of suffering from the disease is higher when the patients have an allele E-4. A significant correlation was found between the presence of the allele E4 and the AD (p < 0.005).