ABSTRACTThe European countries where sewage treatment in waste stabilization ponds is largely developed and commonly used are West Germany (more than 2000 operational systems) and France (about 2500 plants). Portugal has over 50 systems at present and will have about 100 by the year 1993. Spain has more than 10 operational plants and in Denmark there are 50 ponds for tertiary treatment. A survey on the present practice in the countries where the process is largely applied, including size of plants, type of ponds, type of influent and design criteria, is presented. It is found that waste stabilization ponds are particularly appropriate for full treatment of effluents from small communities (less than 5000 population equivalent) and for tertiary treatment following conventional larger plants.