In this paper, a model of the lexicon of Croatian aspectual pairs is presented. The task of this paper is to present the potential of building such a lexicon, highlight the problems that could arise in that construction, and list some possible expansions of the lexicon. At the beginning, the paper describes the theoretical principles necessary for creating such a lexicon. The most important parts of these theoretical principles are the descriptions of morphemes, affixes, different formation processes and verb formation. The paper also reviews semantic categories of verbs. In the next part of the paper, Lexonomy is described as a tool for creating a lexicon and the structure of the entry used in the lexicon is defined in detail. For the purpose of searching the lexicon, the most important elements of that structure are the root and the element that contains the stem from which the verb in the entry was derived. Using these two elements, users can easily find aspectual pairs and other verbs of the same root found in the lexicon as well. Potential problems that can be found in such a lexicon are compounds, ablaut and homonymy, and possible additional extensions that can enrich such a lexicon are the second root, segmentation into affixes, semantic categories of verbs, marking of secondary imperfectives, and expanding the search through other elements.