This article deals with the discussion of using quantitative vs. qualitative methods in a study which aims to describe the lexical competence of Finnish university students of French. It is a longitudinal study which has an interlingual framework. The corpus consists of two parts; the first corpus contains 106 essays, and the second of 50 essays. The latter group represents the control group. The essays are analysed both qualitatively and quantitatively, the latter being the main concern. With this quantitative approach a more objective picture of the development of students’ lexical richness is searched for. In order to make the required calculations, the unit used was to be determined, i. e. ‘word’. Based on results of a pilot test made on one quantitative factor, ‘word’ is defined according to the orthographical definition. In summary, the most important seems to be to have the same criteria throughout the corpus and to be faithful to your own criteria.