This study deals with medical terminology and more particularly with the prefixes and suffixes coming from Latin and Greek which enable the formation of thousands of terms from hundreds of medical roots. The author describes how these forms work in English and in Spanish, and which difficulties may be involved when translating them. She explains the problems that translators have to face when translating medical texts and how they will be able to sort them out easily if they have a good knowledge of these polyhedral and multiuse forms.