During the last twenty years, the concept of informal sector has been extensively studied. These studies have revealed that its extension is associated with an enlargement of the urban poor population which has to develop several strategies in order to survive. Among them are economic and demographic ones. According to studies held in Latin America, households' demographic and economic strategies are closely interrelated, the demographic being the base of the economic one. However, in Africa, the demographic dimension of the informal sector reproduction has most often been ignored. This article is a tentative restitution of this dimension, given its policy implications for the alleviation of the living conditions of the urban poors.