Shriver made the announcement on Twitter today: "Blessed to be able to take Christopher out of the hospital last night. What a feeling of relief to know he's going to be fine."
Schwarzenegger also expressed his joy.
"I knew Christopher couldn't be stopped! Big thanks to all the doctors, nurses & staff at UCLA that helped him recover," he tweeted.
Christopher spent time in the ICU at UCLA Medical Center, where he was treated for multiple broken bones and a collapsed lung, according to TMZ. He is expected to make a full recovery.
Shriver made the call to 911 to summon help for her son when he was injured nine days ago.
"He's awake and breathing," a calm-soundingShriver told an emergency operator as she summoned help to Escondido Beach in Malibu, Calif., on July 17, according to a recording of the call obtained by ABC News Los Angeles affiliate KABC. "He just can't move. He's having trouble breathing."
"A few days ago our son Christopher suffered an accident at the beach," a representative for Shriver said in a statement to ABC News. "While it has been a very scary week, Christopher is surrounded by his family and friends. He is a brave boy and is expected to make a full recovery."
TMZ.com first reported last week that the teenager had been in the intensive care unit "for days" after enduring "multiple broken bones and a collapsed lung" during a surfing accident.
On the recorded emergency call, Shriver described her son's condition.
"It's like a boogie board accident, I think," she said. "He can't move off the beach. Maybe like broken ribs or something like that."
According to a written Los Angeles County Fire Department statement released today, "L.A. County Fire responded [with] an engine, paramedic squad and lifeguards. ... A male juvenile on the beach was treated for an injury and transported to a local hospital with L.A. County Fire paramedics accompanying the patient."
Shriver and Schwarzenegger have been at their son's side through the ordeal in spite of their very public falling out and divorce.
A source close to the family told ABC News that the couple has been "amicable."
"The family remains very close," the source said.
It had been a difficult week for the former couple. According to TMZ, Schwarzenegger is trying to get out of paying spousal support to Shriver and is fighting her request to make him pay for her attorney's fees. TMZ also reported that they had no prenuptial agreement. Their estimated net worth of $400 million would be split between the two of them.
Shriver and Schwarzenegger have moved on since May, when the former California governor revealed that he fathered a child with another woman while married to Shriver and the couple announced their split. The other woman was later revealed to be Patricia Baena, a housekeeper who had worked for the family for years.
Earlier this month, Shriver reportedly bought a $10 million home a few miles from the residence she and Schwarzenegger used to share.
Meanwhile, Schwarzenegger is attempting to revive his movie career. He's signed on to star in "Last Stand" as a disgraced Los Angeles cop. The movie is due out in January 2013.
ABC News' Michael S. James contributed to this report.