Dr. Kenneth Salyer, a craniofacial surgeon, said the surgery on Ahmed Ibrahim went as planned and the child was doing very well, WFAA-TV reported in Dallas.
Ahmed's brother, Mohamed, is to undergo similar reconstructive skull surgery March 9, although it might be delayed because he has the flu.
The surgery will be the last the boys have to undergo before returning to their homeland. The surgeons are using special materials to regenerate bone and close holes in their skulls.
A team of nearly 60 surgeons, nurses and other medical staff separated the boys in October 2003. They had been joined at the crowns of their heads.
Ahmed will be closely monitored for any signs of infection following the 4 ½-hour operation, surgeons said. It may take 12 weeks for the new bone to harden.