The urban populations are young. However, the age groups full resulting from the baby-boom which will enter within the old population the decades to come and will cause an intense demographic ageing and ever equalized, tend to be located in the cities. The urban territories then will be deeply touched by major demographic trends which they never knew and to which they are not prepared. More than one diffusion with the unit of the urban surfaces, demographic ageing will take the form of a wave moving centre town towards the increasingly remote periphery. This completely original space dynamics, imposes a reflexion on the adaptation of urban spaces.Les populations urbaines sont jeunes. Cependant, les classes d'âges pleines issues du baby-boom...