Adults with Down syndrome are at high risk for Alzheimer's disease (AD), with most individuals developing clinical dementia by their late 60s. This increased risk for AD has been attributed, at least in part, to triplication and overexpression of the gene for amyloid precursor protein (APP) on chromosome 21, leading to elevated levels of amyloid [beta] peptides. This article offers a brief overview of our current knowledge of AD in the DS population. In addition, information on an NIA/NICHD-funded, multicenter longitudinal study of biomarkers of AD in adults with DS is provided.