How, according to the folk-tradition, do the Walloons see the Flemish population? An analysis of a stereotype is attempted here, considering the importance of stock-phrases and tags with regard to relations between populations. For an historian, the study of the folk-tradition sets a lot of problems concerning the research and the critical use of a complex documentation: oral tradition (popular phrases, songs, by-words, interviews), French and dialect al literature (navels, dramatic works, satirical writings), newspapers, etc. With such a documentation, we are able to describe some «patterns» of Flemings: the pedlar, the play-character, the militant Fleming, the farmer, the agricultural labourer and the worker. These portraits generally emphasize the dull-witted and rough appearance of the Fleming. The rise of these ideas, at a some time, among the Walloon population appears resulting from the social and cultural position of a great deal of the Flemish immigrants into the Walloon area.