Large deep-seated landslides with a shear surface deeper than 3 m and a mean affected area of 4.2 ha are common features in the Flemish Ardennes. None of these deep-seated landslides are dated, but they are assumed to be rather old (> 100 years). Because most of these landslides are located under forest, aerial photo interpretation commonly used for the creation of landslide inventories is not a suitable tool to map the landslides in the Flemish Ardennes. Therefore, an intensive 100-day field survey was carried out by two geomorphologists in a 430-km(2) study area. This resulted in a landslide inventory map, indicating the location of 135 large deep-seated landslides.