The National Alzheimer's Coordinating Center (NACC) was established by the National Institute on Aging (U01 AG016976) in 1999 to facilitate collaborative research among the 29 NIA-funded Alzheimer's Disease Centers (ADCs) nationwide. NACC developed and maintains a large relational database of standardized clinical and neuropathological research data collected from each ADC, and this database provides a valuable resource for both exploratory and explanatory Alzheimer's disease research.