Medical translation is widely considered as scientific or specialist translation whose main features are its terminology and the lack of stylistic niceties. According to the author the main emphasis in medical translation is solving the terminology, which is the key issue in the text. Through many examples the article analyses the complexity of medical language. The article also looks at the historical reasons for this complexity mainly due to synonymy and polysemy. It also analyses false friends and the influence of old fashion French in Spanish medical vocabulary. The conclusion points out the many risks which translators face because there is no normalisation of technical terms in medicine.