Silene vulgaris s.l., a very polymorphic taxon, has aroused the interest of systematists for a long time; it has also baffled them. Numerous topics remain unresolved on the way to an entirely satisfactory and usable taxonomic solution for floras. Our work relates to 57 morphologic characters and approximately 3000 specimens. To deal with such a bulk of information we chose the method of numerical taxonomy. According to a preliminary study, the characters related to the foliar surface seem important: we therefore used an automatic microprocessor surface analyser. A discussion of the characters selected is presented, together with the general operating chart. This article is the first of a series on this biosystematic study.