Erlang is a dynamically typed concurrent functional language of increasing interest in industry and academia. Official Erlang distributions come equipped with Dialyzer, a useful static analysis tool able to anticipate runtime errors by inferring so-called success types, which are overapproximations to the real semantics of expressions. However, Dialyzer exhibits two main weaknesses: on the practical side, its ability to deal with functions that are typically polymorphic is rather poor; and on the theoretical side, a fully developed theory for its underlying type system --comparable to, say, Hindley-Milner system-- does not seem to exist, something that we consider a regrettable circumstance. This work presents a type derivation system to obtain polymorphic success types for Erlang programs, along with correctness results with respect to a suitable semantics for the language.