The city of Grigny in southeastern France has implemented a mecanism of Participatory Budgeting since 2005. The objectif of this paper is to discuss the place of deliberation in this mecanism. From an open participation in the beggining, linked with an experience of local councils, the mecanism includes more and more projects. To find an effective way of deliberate and vote, the city has implemented since 2010 a system with a preparation by a little group of citizen that pre-evaluate the projects and give an opinion to the participatory council. This solution has the expected result but leads to give less time to collective deliberation on projects. The question is central because its dynamics could give less importance to deliberation. This paper is based on quantitative data and on qualitative observation and interviews.