Naturalization is a translation procedure that is predominantly utilized in the translation of English medical terms into Indonesian. This study focuses on identifying types of naturalization involving the adjustment of spelling and pronunciation and investigating whether naturalization has been appropriately applied based on the rules in the Indonesian general guidance of term formation. The data were taken from the translation of selected articles of a medical textbook, General Ophthalmology (2008). The findings show that naturalization in English-Indonesian medical terms occurred in four categories, namely (1) adjustment of spelling with complex adjustment of pronunciation, (2) adjustment of spelling with simple adjustment of pronunciation, (3) adjustment of pronunciation without adjustment of spelling and (4) adjustment of spelling without adjustment of pronunciation. The products of naturalization have followed the guidance yet several new adjustment standards need to be included to enrich the pattern of foreign term adoption. In addition, this study recommends that types of ‘absorption’ in the Indonesian guidance of term formation needs to be revisited in order to precisely classify how foreign term’s pronunciation and spelling adjustment is made in the Indonesian language. پرونده مقاله