In 1895 the salt mine Friedrichshall (Southwestern Germany) was shut down after a catastrophic water inrush. The following leaching and relocating processes led to a considerable subsidence, whose influences are still significant. In the run-up to the preparation of the building land, the mining authority in 2004 demanded further investigations to assess remaining risks at the surface.A lot of problems - which had to be solved first - were caused by discrepancies between the existing mine maps, particularly with regard to the orientation marks. By the use of digital terrain models, based both on current airborne-laserscans and historical maps, it was possible to describe the course of subsidence.Comparing the former volume of the underground mine workings as well as the volume of the surface depression, a remaining potential of the subsidence could be estimated.Starting from these results a geomechanical modelling led to a differentiated risk assessment for the designated building sites and other areas of influence.