The phenomenon of sex-change operation transsexual patients has been happened since long time ago and continues to this day. But the emergence of differences in legal opinion on this case in particular between Islamic law and civil law, caused/made public confusion, especially those transsexual patients. The Main problems in this study: first, how legal reasoning of civil law and Islamic law on sex-change operation transsexual patients. Second, where is the difference between civil law and legal reasoning of Islamic law on sex-change operation transsexual patients.
To answer these problems, the researcher used a descriptive comparative study with the approach of case study. This study emphasizes on data extracted in the field with a particular technique, and then illustrated in a sentence by categorizing based on character, then taking the conclusions.The Research findings indicate that the background of the emergence of differences in legal sex-change operation transsexual patients between civil law and Islamic law in Indonesia due to the difference between the two legal reasoning. Although they are from the same basic legal issue is about "legal status for people with sex-change operation transsexual" but between civil law and Islamic law is different in the 3 (three) other elements of legal reasoning.
Civil law has no specific legal basis of sex change. But his position to check and decide the case, has directed the judge conducted an analysis using contextual epistemology progressive character of the concrete, objective, and using an inductive approach. By this kind of epistemology allow the emergence of adoption statutes of a sex-change operation for transsexual people when there are certain facts that are legally justified. The Islamic law actually has a legal referral cases of sex-change operation transsexual. However, the use of textualist epistemology with abstract characters, subjective and deductive approach, making MUI prioritize the major premise (the texts/nash) of the minor premise (empirical facts). The impact, the ban of sex-change operation is found by study of the text, apply to all patients regardless of the heterogeneity of transsexual background.