

I saw this a few years ago on "Tomorrow's World" (low-brow BBC
technology news program).  The patient is lowered into a bath of
de-ionized water and carefully positioned.  High intensity pressure
waves are generated by an electric spark in the water (you don't get
electrocuted because de-ionised water does not conduct).  These waves are
focused on the kidneys by a parabolic reflector and cause the stone to
break up.  This is completely painless.

Of course, you then have to get these little bits of gravel through
the urethra.  Ouch!

Paul.
