A 10-year-old girl has been given a vein transplant using a blood vessel grown from her own stem cells.
It is the first time such an operation has been undertaken, marking a milestone in tissue engineering.
Similar techniques may in future offer hope for at-risk patients undergoing bypass surgery.
The girl had a blocked hepatic portal vein, which drains blood from the gut and spleen to the liver.
Without treatment, the condition can lead to serious complications including internal bleeding, spleen enlargement and even death.
Traditionally bypass surgery has been used to restore portal blood flow, using sections of vein taken from other parts of the body. This can cause other problems and is not always successful.
The new technique involved growing a new section of portal vein from the girl's own bone marrow stem cells.
First, a nine centimetre segment of groin vein was taken from a deceased donor and stripped of cellular tissue, leaving a tubular protein "scaffold".
Maturing stem cells were "seeded" into the scaffold, which two weeks later was implanted into the girl's body.
Normal blood flow was restored, but after a year the graft had to be lengthened with another piece of vein made from stem cells.
The girl has remained well since and even managed to take part in gymnastics, the Swedish team reported in the latest online edition of The Lancet medical journal.
The researchers, led Professor Suchitra Sumitran-Holdgersson, from the University of Gothenburg, wrote: "The new stem cells-derived graft resulted not only in good blood flow rates and normal laboratory test values but also in strikingly improved quality of life for the patient."
Because the graft was built from the girl's own cells, it was accepted by her immune system.
Two British experts commenting in The Lancet said the technique looked promising but was yet to be properly tested in clinical trials.
Professor Martin Birchall and Professor George Hamilton, both from University College London, wrote: "The young girl in this report was spared the trauma of having veins harvested from the deep neck or leg, with the associated risk of lower limb disorders, and avoided the need for a liver or multivisceral transplantation."
However they pointed out that the high cost of such procedures might be an obstacle to making them more widely available.