People who donate one of their kidneys are likely to live just as long as those who keep two, a major investigation found.
More than 80,000 live kidney donors were included in the US study looking at the long-term effects of parting with a kidney which concluded there was little risk to the donor.
"Donating a kidney is safe," said leading author Dr Dorry Segev, a transplant surgeon at Johns Hopkins University School of Medicine in Baltimore.
"Live donors start healthy and it's the highest priority of the surgeon and the entire transplant community to make sure they stay healthy. This study says we have succeeded. While there are never any guarantees with surgery, donating a kidney is safer than undergoing almost any other operation."
Dr Segev's team looked at data from a national registry of 80,347 live kidney donors in the US from 1994 to 2009. During the whole 15-year period, there were 25 deaths in the first 90 days after donation surgery, a mortality rate of 3.1 per 10,000 cases.
By contrast the risk of dying after having a gall bladder removed was 18 per 10,000 cases -- roughly six times higher.
The death rate associated with removing a kidney for reasons other than organ donation, such as cancer, was around 100 times greater.
During the time period studied, surgeons switched from mostly open-abdomen to less-invasive "keyhole" procedures.
"Whatever happens when people donate kidneys, on average, it doesn't affect the rest of their lives -- and that has never been shown before in a study of this size and scope," said Dr Segev.
The findings are reported in the Journal of the American Medical Association.