According to lawyer Christopher Dolan, McMath left the hospital in a private ambulance shortly before 8 p.m. Sunday. Dolan says she was taken while attached to a ventilator but without a feeding tube.
The hospital said McMath was released to the coroner, who then released the girl to her mother, per a court order.
McMath, 13, had been on a ventilator for nearly a month at Children's Hospital Oakland. McMath will be taken by the family to an unknown destination, hospital officials said.
A judge cleared the way on Friday for McMath to be moved from the hospital on the condition that the girl's mother must assume full responsibility for the move, including the possibility that her daughter could go into cardiac arrest.
ABC News and the Associated Press contributed to this report.