Large, deep-seated (shear surface deeper than 3 m) landslides are a widespread phenomenon in the Flemish Ardennes (Belgium). The majority of them lie under forest. Some of the landslides are still active or have been reactivated and cause damage to forest and infrastructures. These landslides are characterised by a mean area of 5.1 ha, a mean scarp width of 255 in and an average landslide length of 200 in. 48 % of the landslides is occupying 60 % of the total hillslope length. The spatial distribution of the mass movements is conditioned by the geological setting, the slope gradient (the mean slope gradient of the failed slopes is 0.15 m.m(-1)) and the slope aspect (72 % of the large landslides can be found on slopes with a SW, W or NW orientation). Both the slope gradient and aspect are closely related to the pronounced valley asymmetry in the area, and the river network. Excessive rainfall events or seismic shaking are considered as possible triggering mechanisms. A more detailed analysis is conducted to assess the probability of a seismic cause for these large landslides.