All things being equal medically, if a person is going to donate a kidney is there halachic or hashkafic reason to presume donating one kidney would be better than the other?

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    ת"ר שתי כליות יש בו באדם אחת יועצתו לטובה ואחת יועצתו לרעה ומסתברא דטובה לימינו ורעה לשמאלו דכתיב לב חכם לימינו ולב כסיל לשמאלו — Brachos 61a
    – b a
    Jan 7, 2013 at 1:14
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    @SethJ All things being equal, it is generally easier surgically to take the left kidney, as it has a longer renal vein and the liver is farther away from the surgical area. If the kidneys have unequal function, however, the donor generally keeps the better one.
    – Fred
    Jan 7, 2013 at 3:13
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    @SethJ Also the recipient may have one that is better than the other, so they will want to keep that one and transplant the other.
    – Ariel
    Jan 7, 2013 at 3:27
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    @msh210 Kidneys are not all or nothing. Below 10% they are considered failed, but 10% is better than 0.
    – Ariel
    Jan 7, 2013 at 5:54
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    @Fred, I assumed that "all things being equal" meant health, function, and ease of access/removal. If those things aren't equal, then I'm sure there must be an order of preference from a medical standpoint, but I still find it hard to see how this affects Halachah. I thought the question was about right or left, not better or worse.
    – Seth J
    Jan 7, 2013 at 15:24

2 Answers 2


Asked and answered by the Baba Sali (as quoted in Yerios HaMishkan pgs 12-13)

Someone once asked the Baba Sali which of his kidneys he should donate to a Jew in need of a transplant. After all, Chazal teach that one kidney provides good advice, while the other is somewhat of a yetzer ha-ra. Presumably, the right kidney is the yetzer ha-tov; should he keep that kidney for himself or give it to his fellow Jew? Perhaps it would be wrong to give his left kidney, his yetzer ha-ra, to someone else! The Baba Sali said that he should, in fact, give his left kidney. The very fact that he chose to be moser nefesh for someone else would change his yetzer ha-ra into something good!

(I assume in the ma'aseh that all things were equal medically).


Thanks for the above comments on medical preference. Just to extend that a bit -- even if there was zero medical preference on the kidney's utility for the recipient (which is likely incredibly rare), my next thought would be about the long-term health of the donor -- is s/he will only have one kidney, an injury to it would be life-threatening. Thus, on which side is a kidney likely to be better-protected from damage? (Probably ask a trauma surgeon what they see most often.)

  • Good edit. [15]
    – Seth J
    Jan 7, 2013 at 15:59

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