Doctors say one of the Egyptian twins born joined at the head has sat up for the first time in his life following separation surgery last week.
Neurosurgeon James Thomas at the Children's Medical Center in Dallas, Texas, said Tuesday two-year-old Mohamed Ibrahim is breathing on his own and is more active and alert than his brother, Ahmed.
He said Ahmed may be removed from a ventilator later Tuesday.
Dr. Thomas said each of the boys is following a different path of recovery, adding that both remain in critical but stable condition.
A team of doctors worked 34 hours last week to separate the children.
Ahmed and Mohamed were born in a village 800 kilometers south of Cairo. They have been in the United States for more than a year preparing for the surgery.
Meantime, doctors in New York say they have successfully completed the first of at least three operations to separate Filipino twins born joined at the head. Surgeons inserted devices to stretch the skin on the heads of 18-month-old twins, Carl and Clarence Aguirre.