Soil erosion by water is considered to be one of the most important land degradation processes in Mediterranean Europe. Over the past decades most studies dealing with water erosion in this environment have mainly focussed on interrill (sheet) and rill erosion. However, recently collected data in the framework of the MEDALUS project (Mediterranean Desertification and land Use) point to gully erosion as a very important sediment source: 50 to 80 % of total sediment produced in upland areas originates in ephemeral gullies. Given that gullies are effective links between upland areas and channels, gully erosion aggravates flooding problems and the silting up of reservoirs. Consequently, more attention should be given to the prediction of sediment production by ephemeral gullying under a range of environmental conditions. In order to predict soil losses by ephemeral gully erosion, the model EGEM (Ephemeral Gully Erosion Model) has been tested. EGEM has two major components, of which the hydrology component is a physical process model based on the runoff curve number. The erosion component uses the hydrology outputs to solve a combination of empirical relationships and physical process equations in order to compute the final width and depth of the ephemeral gully. An EGEM-input dataset for 86 ephemeral gullies was collected in cultivated lands in Southeast Spain and in both cultivated and abandoned lands in Southeast Portugal. A first analysis indicates that EGEM tends to underpredict soil losses by ephemeral gully erosion, probably because of the stony nature of most soils in the study area. However, an important input parameter for this model is total ephemeral gully length which is seldom available. Hence, threshold relationships between local slope gradient and drainage area for the beginning and ending of ephemeral gully trajectories have been established in a variety of Mediterranean environments in order to predict total ephemeral gully length. Despite the various physiographic conditions, landuses and storm characteristics in the studied areas, the results indicate a potential of the topographic threshold concept to predict the location of ephemeral gullies.