<?php
...
$ok = 0

echo '<script language="JavaScript">';
echo'confirm("Voulez vous vraiment supprimer cet enregistrement!");';
echo'if(confirm)';
echo'<?php $ok = 1; ?>';
echo '</script>';
if ($ok == 0)
exit;
...
?>

If s.o. knows what's php's exit in javascript, it also can be too helpfull.
Thanks Anyway

You cannot mix PHP and JS like that, they are two different technologies run at two different times. JS is run on the client, and PHP is run on the server so they can't directly interact with eachother.

You'll have to make a new page with an HTML link that passes the data through the query string (or something similar), for example:

Voulez vous vraiment supprimer cet enregistrement!
<a href="thispage.php?ok=1">OK</a>
<a href="thispage.php?ok=0">Cancel</a>