Celebrity Cruises said the Celebrity Millennium's closed-circuit video shows the woman climbed over a railing Monday night and let go.
The Celebrity Millennium, which can carry as many as 2,000 passengers, was on its way from Cabo San Lucas to Vancouver, British Columbia. When the ship docked in San Diego on Tuesday, the woman was not on board.
The U.S. Coast Guard was called in as soon as the woman was declared missing. She was last seen aboard the ship Monday night.
The company said the ship's GPS satellite marked the location where the guest went overboard.
The Coast Guard searched about 25 hours over more than 1,900 square miles before suspending the operation without finding the body.
The Associated Press contributed to this report.