The LOAD collection is a longitudinal, multi-center late onset AD sibling genetics initiative. This NIA-funded study began in 2002 and maintains DNA and cell lines on families with 2 or more siblings with AD (at least one probable or confirmed AD) (n=5291). A third family member who is either affected or unaffected is also required. These individuals are evaluated in person and/or over the phone. A minimum dataset is collected for each person in the family. Definite AD is defined by established neuropathological criteria (and confirmed by autopsy). Probable or possible AD is defined according to NINCDS-ADRDA criteria. Autopsy is offered to all subjects.