The surgery was successful, a source told the Houston Chronicle. The source, described as familiar with the case, said Giffords was recovering in the intensive care unit at Memorial Hermann Hospital.
The Arizona Democrat had the surgery at Memorial Hospital while her husband, astronaut Mark Kelly, was in space, ABC News reported. Kelly, who commands the final mission of the shuttle Endeavour, docked Wednesday with the International Space Station.
A section of Giffords' skull was removed shortly after she was shot in the head in January during a constituent event in Tucson. Jared Loughner, a college graduate, has been charged with killing six people and wounding 13 in a mass shooting aimed at Giffords.
Dr. Nicholas Boulis, a neurosurgeon at Emory University Medical Center in Atlanta, said the section of the skull would have been removed to allow Giffords' brain to swell outward. If the brain had remained confined in the skull, it might have caused a fatal injury by swelling inward.
In many cases, surgeons re-insert the original bone, ABC said. Giffords' doctors used a plastic implant custom-fit to the hole in her skull.