MLB Hall of Famer Tom Seaver Diagnosed with Dementia

Hall of Fame pitcher Tom Seaver has been diagnosed with dementia and "has chosen to completely retire from public life" ... his family announced Thursday.

Seaver -- a World Series champ, 13-time All-Star and 3-time Cy Young winner -- played in the majors from 1968 to '86 ... and was a first-ballot entry into Cooperstown.

"Tom will continue to work in his beloved vineyard at his California home" the statement says ... explaining that he will no longer make public appearances.

"The family is deeply appreciative of those who have supported Tom throughout his career, on and off the field, and who do so now by honoring his request for privacy."

Seaver is one of the greatest to ever wear a Mets jersey -- he had his No. 41 jersey retired in 1988 and was given the nicknames "Tom Terrific" and "The Franchise" during his playing days.

Seaver also played for the Reds, White Sox and Red Sox ... raking in 311 wins.