According to the new institutionalist literature, the rules regulating a decision making process play great influence on its final result. Thisassumption applies to the 1987-1988 National Constituent Assembly (ANC). Otherwise, a group of legislators dissatisfied with the works course would not have risen with a proposal to reform the Internal Rules after two years of Assembly. The main goal of this work is tocomprehend the importance of the institutional structure for the political contests and the final result of the NCA. Thus, I aim to answer the following question: what are the effects of the rules regulating the convocation of the NCA, as well as the rules regulating its works which have changed during theprocess on the final results? The constitution-making design approved at the beginning (a congressional one instead of an exclusive one) and the organization form of the works (decentralized in thematic commissions) were largely contested because of the consequences political actors were anticipating and looking forward to, since they are always aware of the rule´s impact. The question is whether or not they anticipated it correctly, and for such it is possible to watch how they have behaved. Attempting to deepen the debate about strategic interaction on the constitutional process, the roll calls will be analyzed in order to understand how collective actors organize their preferences, building majorities in radicalized political contests.