Doctors at Children's Medical Center Dallas spent the night separating the intricate connection of blood vessels running between the brains of Ahmed and Mohamed Ibrahim — considered the riskiest part of the operation.
They were separated at 11:17 a.m. Sunday, hospital officials announced later in a prepared statement.
"They are now within striking distance of living independent lives," said Dr. Jim Thomas, chief of critical care at the hospital.
The next procedure could take as long as six hours and will involve reconstructing their skulls and covering the wounds with skin, Thomas said.
Doctors have spent more than a year planning the surgery, which doctors had said could last up to 90 hours. Eighteen doctors were involved, along with 30 to 40 other medical personnel.
Extra skin created by skin expanders inserted in the boys' heads and thighs five months ago will be used to cover the head wounds.
The boys were born June 2, 2001, by Caesarean section to Sabah Abu el-Wafa and her husband, Ibrahim Mohammed Ibrahim.
Dallas-based World Craniofacial Foundation, a nonprofit group that helps children with deformities of the head and face, arranged to bring the boys to Dallas in June 2002 for an evaluation.
A team of specialists determined the boys could be separated, though the risks include possible brain damage and death. The boys' father told doctors he felt it was worth it to give them a chance at a normal life.
The father spent much of the past year in Dallas with the boys before returning to Egypt this summer. He returned this week with his wife and the twins' young brother, Mahmoud.
Thomas said the parents were "doing fine."
"I think the parents are helped in many ways by a very strong faith structure that they have," he said.
"They have said repeatedly to all the parties involved that this is in God's hands."