From question of fact to question of law to question of private international law: the question whether a person is male, female, or ... ?

Some countries have introduced a third sex other than male and female as a status. This shows that the sex allocation and status registration is not only a question of fact but can also contain legal elements. This characterization leads to consequences for private international law (PIL) issues. The article analyses the consequences for a person that legally acquired a third sex status (X, or "other", or "vacant field") coming into contact with a legal system that is not aware of the third option, for example, in cases of marriage or parenthood. So, the question is whether the second legal system can "accept" the unknown legal status, as it does in other cases of unknown foreign status. The influence of the European Convention on Human Rights and of EU law on the one hand and public policy on the other hand can be relevant. In cases where acceptance is granted, the question arises how to treat said person under a national law that does not know the determined sex. Usually, recognized foreign legal phenomena unknown in the national system lead to an adaptation of the rules by the PIL means of transposition. This article proposes solutions that balance recognition rules, status law, and personal interests of the person involved.