Former French president Jacques Chirac, 83, was admitted to hospital on Sunday with a lung infection, his son-in-law said.
Chirac, who led France from 1995 to 2007, was "hospitalised this morning at Pitie-Salpetriere (hospital in Paris) to be treated for a lung infection," Frederic Salat-Baroux told AFP, adding he would remain there "in the coming days."
The popular ex-president had just returned from a visit to Morocco, Salat-Baroux added.
A source close to the former president confirmed that he was conscious.
Chirac, who served two terms as head of state, is probably best remembered internationally for his opposition to the US military intervention in Iraq in 2003.
A small stroke while in office in 2005 weakened him, and he is now rarely seen in public.
In December 2015, he spent two weeks in hospital, suffering from what his family described as fatigue.
In recent weeks, his entourage said his health had improved.
Chirac has reportedly suffered from a degenerative neurological disorder in recent years, leading prosecutors to spare him the embarrassment of having to appear in court during his 2011 corruption trial.
He was handed a two-year suspended prison term for colluding in the creation of 28 fake jobs for party workers when he served as Paris mayor.