The growing global disease burden attributable to dementia has strongly stimulated research activities. However, patients with dementia that are included in clinical research are systematically younger than patients from the general population. This large age gap perhaps indicates a lack of methodological rigour, but, more importantly, has the potential to affect the interpretation of research finding-eg, those relating to neuropathology, apolipoprotein E polymorphisms, the effects of cholinesterase inhibitors, and many other issues relevant to patients with dementia. Research on dementia has a lot to gain from the study of patients that more appropriately reflect the population at risk.