The aging of the population is a worldwide phenomenon, and studying age-related diseases has become a relevant issue from both a scientific and a public health perspective. This review summarises the major findings concerning prevention of Alzheimer's disease (AD) and other dementias from a population-based study, the Kungsholmen Project. The study addresses risk- and protective factors for AD and dementia from a lifetime perspective: at birth, during childhood, in adult life, and in old age. Although many aspects of the dementias are still unclear, some risk factors have been identified and interesting hypotheses have been suggested for other putative risk or protective factors. At the moment it is also possible to delineate some preventative strategies for dementia.