Although dementia is usually a late-life syndrome, it is now well known that pathological changes begin quite early in adulthood, outside the classical age borders of geriatric specialties. In order to design effective preventive strategies, adequate information can only be gathered by taking a life-long view of Alzheimer's disease (AD). Dementia risk is the result of exposure to both harmful and protective factors along the life course, and these factors, as well as their impact on the individual's health status, change over time. This review aims at presenting current epidemiological data on serum cholesterol levels and dietary fat intake as risk factors for dementia/AD, and at discussing the reasons and significance of contradictions between various studies. Reducing dementia risk may be possible by influencing the serum lipid profile. A more detailed characterization of the mechanisms behind the association of cholesterol (in both serum and brain) with dementia/AD, mechanisms about which little is currently known, would allow a better translation of research findings into clinical practice.