Loan words compose a particular chapter in the field of translation. The current book has been set out to investigate the phenomenon of loanwords in medical translation. To achieve depth in the analysis, we are going to investigate the presence and the use of loanwords, in medical terminology. The language pair that we examine is from English to Greek and vice versa. We examine the type, the style, the register, the grammatical and syntactical structure of the texts, with the use of some examples. We highlight various definitions of loanword, calque and loan translation. Furthermore,we present a historical review of the English, Greek and Latin language through centuries. Finally we refer to some methodology techniques followed by translators and linguistics all over the world.