The topic of this article is variation and linguistic changes in the Danish insular dialects (i.e. the dialects of Zealand, Falster, Lolland, Funen and surrounding islands) at the end of the nineteenth century. It has been claimed that dialect levelling within this period most likely is the result of horizontal convergence. This article argues that the developments should rather be seen as manifestation of vertical convergence though the changes within this period often lead to compromise forms. The sources used are Ømålsordbogen (i.e. Dictionary of the Danish insular dialects) and its collections. The article also discusses methodological problems in using this kind of data.