Hargitay, who is the daughter of late Hollywood actress Jayne Mansfield and one-time Mr. Universe Mickey Hargitay, is best known for her work on the television drama "Law & Order: SVU."
TMZ said Mariska Hargitay suffered a partially collapsed lung during the Christmas holiday and then again Monday.
She reportedly has been readmitted to the hospital, but the entertainment news Web site said the cause of the problem and her condition were unknown.
Her publicist confirmed to TMZ only that the actress has suffered a partially collapsed lung but she isn't expected to miss taping any episodes of her show this season.
Hargitay was nominated for a Golden Globe for best actress in a TV drama, but lost Sunday to Anna Paquin of "True Blood."