Press secretary Robert Gibbs said in a statement that Obama was inadvertently struck by an elbow. The elbow's owner wasn't identified.
Obama received the stitches under local anesthesia in the doctor's office on the ground floor White House after he returned home.
The president had traveled to nearby Fort McNair to indulge in one of his favorite athletic pursuits, basketball. It was a five-on-five contest involving family and friends and including Reggie Love, Obama's personal assistant who played at Duke University.
Obama emerged from the building after about 90 minutes of play, wearing short-sleeve T-shirt and gym pants, and was seen dabbing at his mouth with what appeared to be a wad of gauze. A few hours later, reporters who had gathered on the White House driveway for the arrival of the Christmas Tree saw the president in an upstairs window, pressing something white against his mouth.
"After being inadvertently hit with an opposing player's elbow in the lip while playing basketball with friends and family, the president received 12 stitches today administered by the White House Medical Unit," Gibbs said.
