Many sanitary and storm sewer networks are old and deteriorating rapidly. Water and sanitation managers are becoming more and more aware of the negative impact of poorly maintained sewer networks, especially since they are asked to comply with stricter environmental standards under already challenging budget constraints. The best way to improve the structural condition of a sewer network is to replace failed pipe sections. Planning replacement works necessitates knowledge of the present structural state of the network and of the evolution of this state in the near future. Towards this goal, a predictive modelling strategy was developed for the structural state of a sewer network. A case study in a Quebec municipality is presented to illustrate how the modelling strategy developed can be used to simulate the evolution, over the next 20 years, of the length of a sewer network in poor state, and to assess the impact of different replacement strategies on the global state of the network.Key words: urban infrastructures, sewers, structural state, modelling.