The Mostolés-born stopper shipped only 32 goals in 36 games this season - the same as last year's winner, Roberto 'Pato' Abbonzanieri of Getafe.
He said to the Real Madrid website after receiving his award, "The truth is that I'm very excited by this. But this is an award that I must share with the rest of the team, who have been fantastic all season. Without them I could not have done it.
"Nobody likes conceding goals and that's especially true of goalkeepers, but given the average of recent years I'm not complaining about this total. Plus, Real Madrid always attack. That's why we need to give credit to the defenders and the whole team - we all attack so we all must defend, and that's what gave us this total."
Casillas is a special case among Madrid 'keepers for this reason, as the stopper himself noted.
"Being a low-conceding 'keeper at Madrid is difficult for the attacking reasons, as well as others such as pressure and the need to concentrate.
"It's been 16 years since a Madrid 'keeper won? That's a long time. I believe that a Madrid goalie must always fight for this award, just as the strikers aim for the 'Pichichi' trophy. That's good for the team, and means that we're fighting for the Liga as well as other tournaments.
"My message to the other 'keepers? The same as I've said: this is a great honour and a source of pride. They won it before and I know from experience how hard one must fight and work to gain it. For me, as a goalkeeper and a Madridista, I'm proud to have followed those who made history."
Steve Michaels, Goal.com