The commonly used Catalan lexicons (DCVB, DECLC, the vocabulary of Lluís Faraudo de Saint-Germain) collect words and give them meaning from ancient editions of texts. Lexicographers? performance had its own logic: they used the documentary sources they had at their disposal when they set up to write their works. The advances in philological research (new critical editions, new sources of information) allow us to refine results and detect errors that occurred in old editions and went into dictionaries. Wrong lexemes were included, as well as incorrect or insufficient definitions. This article offers examples of it, out of four medical works. On the one hand, the Catalan translations of the Regiment de sanitat (1305-1310) by Arnau de Vilanova, and of misser Joan?s Llibre de receptes (1466), both widely used by lexical repertoires. On the other hand, the Catalan translations of Hippocrates?s Aphorismata and of a fragment of Bernard of Gordon?s Lilium Medicinae, both of which our lexicographers ignored, as they have been first published only recently.