The printer Gheraert Leeu, active at Gouda from 1477 to July 1484, and thereafter at Antwerp to 1492, is known as a remarkably successful figure in his trade. To allow a more exact specification of the factors that led to his success, the present article presents a hibliometric analysis of his publications. This analysis also serves to raise questions about the methodology to be used. The measurement of a publisher's output on the basis of the number of editions turns out to have a limited value; counts based on the number of edition-sheets lead to different and in some respects better results. The latter should ideally be supplemented with information about the edition sizes. If one wishes to study a publisher's output in relation to the content of the books, then one needs not only a universal division into subjects or genres, but also a classification suited to the particular period. For this study of a fifteenth-century publisher, a division according to mediaeval 'dimensions' yields good results. The quantitative information this approach provides about Leeu's publications paints a picture of this printer as an entrepreneur who reacted to changing economic circumstances with some success. This did not, however, allow him to escape the general trends. An economic crisis around 1482 led to a decline in Leeu's production along with that of other printers. Leeu's production at Antwerp especially shows that he followed general practice by reducing the average size of his books while increasing the number of editions he put on the market. In spite of that, the average number of edition-sheets produced annually declined so much that it would have taken a large increase in the edition sizes to compensate for it. In the content of his Antwerp publications, Leeu shifted his emphasis from texts with moralistic, narrative or religious dimensions to texts with a more practical content.