Alzheimer disease and allergic diseases are common health problems. The aim of the study was to check the hypothesis that older patients with IgE-mediated allergies have a higher prevalence of Alzheimer disease. It was a retrospective, multicenter cohort observation. In total, 7129 people were examined, including 3566 women and 2558 men (mean 64.9±6.9 y). The diagnosis of Alzheimer disease is based on the ICD-10 code and appropriate medical documentation. The proportion of patients with confirmed Alzheimer disease in the group of patients with diagnosed allergy compared to the group of those without allergy was as follows: 13.9% (168) versus 8.2% (484) with P=0.001. There was a positive correlation between the presence of Alzheimer disease and high serum total IgE, eosinophilia, and asthma or the presence of atopic polymorphic disease (P<0.05). IgE-dependent allergic diseases, in particular allergic asthma, and the presence of high serum IgE levels may favor the development of Alzheimer disease.