This article presents a preliminary analysis on the relation between social movements and political institutions, a subject which has not been sufficiently explored by literature. The analysis is based on a case study on the relationship between the housing movement in Sao Paulo and the Marta Suplicy government (2001-2004), and from the Workers' Party (PT). The discussion is divided in two parts: in the first one, we develop the argument that the relationship between social movements and the political system is permeated by an intrinsic tension between the principles of autonomy and political efficacy. In the second part, we explore this discussion relating it to the specific dilemmas that bound participation in the city of Sao Paulo, using the housing movement as an empirical reference.