The problem of guessing a random string is revisited and some prior results on guessing exponents are re-derived using the theory of large deviations. It is shown that if the sequence of distributions of the information spectrum satisfies the large deviation property with a certain rate function, then the limiting guessing exponent exists and is a scalar multiple of the Legendre-Fenchel dual of the rate function. Example applications re-deriving prior results are also given.