The aim of this paper is to show what Lexicography and Dialeclology have in common, despite the fact that these two disciplines might appear to be rather disparate in their main goals and methodology. The occurrence of dialectal expressions in general purpose Spanish dictionaries as well as the creation of a range specifically dialectal terms within the regional variants of the language are analysed. Regarding the latter, special emphasis is placed on the study of dictionaries of Americanism. Both types of expressions are aproached historically and within the Hispanic domain.