The 36-year-old was taken to the Clinique Monceau late on Wednesday and was operated on by brain specialist Stephanie Delajoux.
Gainsbourg had been suffering from headaches for several weeks following a water-skiing accident in the U.S. last month.
The actress' husband, actor/director Yvan Attal, said his wife was improving as he left the Clinique on Thursday to pick up their two children from school.
He said, "She is doing fine. I spoke to her, she replied and I kissed her. She is fine. It's not as bad as the media says it is. She may be able to leave the hospital within the next couple of days."
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