Japan's Kyoto University Hospital says it has successfully conducted the world's first simultaneous lung and liver transplant from living donors.

Professor Date Hiroshi and his team made the announcement at a news conference on Monday.

They said the surgery was conducted last November on a boy under the age of 10, who had a serious congenital disease.

The team said the patient received parts of his parents' lungs and his grandfather's liver.

They added the surgery took more than 18 hours, using four operating rooms. The boy left the hospital this month, after he regained the ability to walk on his own.

The team also said the parents, who are in their 40s, and grandfather, who is in his 60s, have already been discharged from the hospital.

The hospital says that outside of Japan, at least 20 cases of simultaneous lung and liver transplant surgery involving brain-dead donors have been performed. It says this is the world's first case of simultaneous lung and liver transplant to be conducted with living donors.

Professor Date said this transplant is significant because it demonstrates the possibility of transplants for patients with damage to multiple organs.

The boy's parents said they would be happy if their son's case becomes a ray of hope for organ transfer patients and their relatives.