Reflections on terminological variation in scientific Spanish, and an example based on the English term delusion Abstract: Scientific and technical Spanish is not without terminological variation, as a result of historical, conceptual, lin - guistic and social factors. Scientific-technical translators, when they are non-expert mediators in the process of specialized bilingual communication, cannot disregard the reasons that underlie terminological variation, and should have at their dispo- sal a model and the necessary tools to document their choice of term in Spanish. Understanding these factors helps translators to chose the most appropriate term for a specific context, and helps terminologists to systematize discipline-specific concepts and harmonize them across different varieties of Spanish. This article presents an analytical framework for cases of termi- nological variation that is intended to facilitate decision-making by scientific-technical translators. Taking the English term delusion as an example, we identify the factors that have given rise to different translations (delusion, delirio, idea delirante) that have appeared since the term was first used in the field of psychiatry, and describe how globalization has induced recent efforts toward terminological convergence.