The 75-year-old "Rhinestone Cowboy" singer said he decided to go public now with the diagnosis because he is planning a series of live farewell performances this fall and wants his fans to be aware of his condition.
"Glen is still an awesome guitar player and singer," his wife Kim told the magazine. "But if he flubs a lyric or gets confused on stage, I wouldn't want people to think: 'What's the matter with him? Is he drunk?'"
"I still love making music," Campbell added. "And I still love performing for my fans. I'd like to thank them for sticking with me through thick and thin."
In addition to his music, Campbell is also famous for co-starring opposite John Wayne and Kim Darby in the original "True Grit" film.