Former South African president Nelson Mandela was admitted to hospital on Saturday for treatment for a "long-standing abdominal complaint", the government said.
A statement said the 93-year-old anti-apartheid leader needed specialist medical treatment. It wished him a speedy recovery, but provided no further details.
Mandela, who is known to be in frail health, spent several days at Johannesburg's Milpark hospital just over a year ago with respiratory problems.
Since then he has not appeared in public, and has spent his time between Johannesburg and his ancestral village of Qunu in the impoverished Eastern Cape.
As South Africa's first black president, Mandela occupies a central position in the psyche of a country that was ruled by the 10 percent white minority until the first all-race elections in 1994.
Earlier this month, President Jacob Zuma and the central bank issued a new set of bank notes bearing his image.
Mandela has long since withdrawn from active participation in politics and public life in Africa's biggest economy, having stood down at the end of his first term in office in 1999.
His last major public appearance was in July 2010 at the final of the World Cup in Johannesburg's Soccer City stadium.