That was wrong in more than one way. They are about 1.4 Billion adherents, and the largest religion is Christianity with 2.3 Billion, but the catholics are just a portion of that (admittedly more than half but they are not the largest religion). Muslims are 1.9 Billion... So, they are right up there... but if you sect them off you have to split that number up too...Head of the largest religion on the planet with over 2 and a half billion adherents.