It is sometimes held that there is something in the very nature of religious pluralism that undermines the rationality of religious belief. This view, I am happy to note, is beginning to receive the sort of attention it deserves from philosophers of religion. Various arguments from religious pluralism against religious belief have recently been canvassed. But in all this activity, as in the relevant historical discussions, one argument – a probabilistic argument from pluralism – seems largely to have escaped notice. In what follows I develop and discuss a version of the argument, and give an estimate of its force. As I hope to show, it is not an argument to be taken lightly.