In the discipline of terminology, a distinction is made between different types of terminological competences, such as systematic terminology and ad-hoc terminology. The former is defined as the ability to create multilingual glossaries from specialized translations, and the ability to perform terminology management tasks applied to translation, incorporating corpus linguistics tools, performing terminology extraction, building terminology databases, and carrying out computer- assisted translation and machine translation tasks. Ad-hoc terminology is defined as the competence that a specialized translator should have in order to solve terminology problems that arise in a specialized translation. There is much less literature concerned with describing and systematizing this competence, and these approaches come from the field of terminology: Arnzt & Picht (1982), C & eacute;lestin et al . (1984), Cabr & eacute; (2004), Teb & eacute; & Pissolato (2019), Franco (2020). Translatology studies have traditionally paid little attention to ad-hoc terminology since they do not categorize terminological problems in translation as a singular entity that requires particular attention. This article presents a proposal for defining and systematizing the competences that a specialized translator should have when acting as an ad-hoc terminologist. The corpus of texts used to illustrate the competences consists of different scholarly articles in English in the field of biomedical sciences (review articles and experimental articles), translated into Spanish by different cohorts of a translation Master's level students.