Former South African President Nelson Mandela, 94, is back home in Johannesburg after spending the night in hospital following a check-up.A statement by the president's office said that he had undergone a successful, scheduled medical examination at a clinic in Pretoria."He is well and as before," the office added on its website.Mr Mandela spent 18 days in hospital in December, undergoing treatment for a lung infection and gallstones.His health has been a cause of concern for many years.He was admitted for the check-up at a Pretoria hospital on Saturday afternoon.Mr Mandela served as South Africa's first black president from 1994 to 1999 and is widely regarded as the father of the nation for leading the struggle against apartheid and for democracy.He first contracted tuberculosis in the 1980s while detained in Robben Island prison.He has been admitted to hospital on three occasions in the past two years. In January 2011, he was treated for a chest infection in Johannesburg.During his December stay in hospital, President Zuma at one point described his condition as "serious", but added that he was responding to treatment.The former president has been rarely seen in public since retiring from public life in 2004.