"My diary and my public activities will as from today be severely and significantly reduced," Mandela said in Johannesburg.
He spent 27 years in prison but came out to become South Africa's first black leader in 1994. He stepped down in 1999, but has not been idle since.
Mandela was very active in the fight against HIV/AIDS, which affects some 5 million South Africans. As well as flying recently to Switzerland to lead South Africa's bid to host the 2010 soccer World Cup, he also attended Spain's royal wedding and met U.S. boxing promoter Don King in recent weeks.
"I am confidant that nobody here present today will accuse me of selfishness if I asked to spend time while I'm still in good health with my family, my friends and also with myself," said the Nobel peace prize winner.