A medical lexicon of 14013 pairs of technical word forms and the corresponding simplified synonym or definition. It is aimed at automatic text simplification in Spanish. A subset of the lexicon (4642 term entries) was also normalized to Unified Medical Language System (UMLS) concept unique identifiers (CUIs). Note that the number of inflected forms was reduced after revision by experts, with regard to the version used in the published article (Campillos-Llanos et al. 2024). This dataset was collected in the CLARA-MeD project, with the goal of simplifying medical texts in the Spanish language and reduce the language barrier to patient's informed decision making. In particular, the project aims at developing linguistic resources for automatic medical term simplification in Spanish; and conducting experiments in automatic text simplification.