In studying determinants of cognitive aging and neurodegenerative diseases such as dementia, focus in research has mostly been on genetic background and lifestyle factors in adulthood. Over the past two decades, though, it has become increasingly clear that the foundations for brain functioning in later life are laid down in utero and adverse conditions during the prenatal period may increase the risk for the development of premature cognitive decline and neurodegenerative diseases. In this chapter, preclinical as well as clinical research that has provided evidence for prenatal influences on cognitive aging will be discussed. Especially in humans, the number of studies examining the effects of prenatal factors on cognitive aging and dementia is still limited. Evidence from studies such as the Dutch famine birth cohort study, though, suggests that factors such as undernutrition in pregnancy influence brain development and accelerate aging of the brain with negative repercussions for cognitive function and risk for dementia in later life. The evidence for a role of prenatal factors in cognitive aging is discussed in the light of the reserve capacity model, and potential underlying mechanisms are briefly reviewed. Finally, experimental studies in rodents suggest that the negative effects of adverse circumstances in early life are reversible. This is highly important and merits further investigation, especially since the number of prenatal factors that may influence cognitive aging is potentially large and may include factors such as maternal obesity and depression, and prenatal exposure to challenges of the immune system and air pollution. Improving these adverse prenatal circumstances may improve cognitive function in later life and decrease the risk for neurodegenerative diseases such as dementia.