Former Supreme Court Justice Sandra Day O'Connor testifies before the Senate Judiciary Committee hearing on 'Ensuring Judicial Independence Through Civics Education' on July 25, 2012 in Washington, DC.

Sandra Day O'Connor, the first woman on the Supreme Court, says she has the beginning stages of dementia and "probably Alzheimer's disease."

O'Connor made the announcement in a letter Tuesday. She said that her diagnosis was made "some time ago" and that as her condition has progressed she is "no longer able to participate in public life."

O'Connor, 88, was nominated by President Ronald Reagan and took her seat on the court in 1981. She announced her retirement in 2005.

O'Connor's announcement came a day after a story by The Associated Press that she had stepped back from public life.