This dissertation deals with the processing of relative clauses, and focuses on resumptive structures in Brazilian Portuguese (BP). It is grounded on a theory of language processing and acquisition that aims at reconciling a minimalist view of language with psycholinguistic models of sentence processing. The working hypothesis of this study is that there is a correlation between the presence of a resumptive pronoun and processing cost of the relative clause in sentence production, which is defined in relation to the variable focus. As far as comprehension is concerned, there is controversy with regard to the effect of the resumptive pronoun in children`s performance. In this study, two experiments are reported. The first one aimed at investigating the effect of a resumptive in thematic assignment, in relative clause comprehension by BP speaking 3 and 5 year olds. In the second one, an elicited production task was used with BP speaking adults in order to test the hypothesis of resumptives as a last resource strategy in oral sentence production. The results of the first experiment reiterate the effect of focus, but do not support the view that the resumptive pronoun has any facilitative effect. On the contrary, its presence seems to pose difficulties for 5 year olds. The results obtained with adults show a higher frequency of resumptives in right-branching sentences, in those conditions predicted to be the most demanding ones. These results are compatible with the hypothesis of resumptive relative clauses as the result of last resource strategy in language production.