See Pakistan's Musharraf: Bin Laden probably dead

Pakistan's president says he thinks Osama bin Laden is most likely dead
because the suspected terrorist has been unable to get treatment for his
kidney disease.

[A Bush administration official] said U.S. intelligence is that bin
Laden needs dialysis every three days and "it is fairly obvious that
that could be an issue when you are running from place to place, and
facing the idea of needing to generate electricity in a mountain
hideout." [CNN]
Renal dialysis -- talking about hemodialysis -- is something that really
is reserved for patients in end-stage renal failure. That means their
kidneys have just completely shut down. The most common cause of
something like that would be something like diabetes and hypertension.
Once that's happened, if you're separated from your dialysis machine --
and incidentally, dialysis machines require electricity, they're going
to require clean water, they're going to require a sterile setting --
infection is a huge risk with that. If you don't have all those things
and a functioning dialysis machine, it's unlikely that you'd survive
beyond several days or a week at the most. [CNN]