One of a pair of formerly conjoined Egyptian twins underwent surgery on Monday to reconstruct his skull, in what doctors said was an important step to recovery after being separated from his brother in October 2003.

Three-year-old Ahmed Ibrahim was reported in good condition following the four-hour operation, intended to close the hole left in his skull by the separation surgery. The twins had been joined at the head.

“The doctor says he is doing great,” said Susan McBee, spokeswoman for Medical City Children’s Hospital in Dallas, where the surgery was performed. “Everything went exactly according to game plan.”

Brother Mohamed will undergo the same operation next month, she said.

The boys have worn helmets since their separation to protect the uncovered part of their brains, but they are walking and talking and displaying normal behavior for children their age, doctors say.

In Monday’s operation, doctors covered the open portion of Ahmed’s skull with a substance to promote bone growth and added bone material taken from the boy’s thigh.

The twins were born to a husband and wife in southern Egypt and were brought to Texas for treatment by the World Craniofacial Foundation.