Matthew McConaughey and Camila Alves welcome baby daughter
The couple opted against learning the gender of their baby beforehand, celebrating the "wonderful surprise" as they did with their older children, Levi, 4, and Vida, who turns 3 Jan. 3.
No other details about their new addition have been released, including the baby's name and weight.
The emaciated actor's own dramatic weight loss has been the subject of much scrutiny in recent months, as he shed at least 30 pounds for his role as a 1980s AIDS patient in "The Dallas Buyers Club," which began filming last month.
McConaughey and Alves, a Brazilian model, have been together since 2006 and tied the knot in June 2012.