A New South Wales law determining how sex is represented on birth and death registrations will be tested in the High Court today.

The case was sparked by Sydney resident Norrie who wants to be recognised as being of non-specific sex.

Norrie was born in Scotland as a male, and underwent sexual reassignment surgery in 1989.

Norrie identifies as neither male nor female.

In 2010, Norrie applied for a name change and to be registered as being of non-specific sex.

At first the NSW Registrar of Births, Deaths and Marriages agreed, but then the decision was revoked.

Norrie was told it was beyond the power of the law to recognise options beyond male and female.

With the application for a change of name, Norrie was told the entry for sex would be "not stated".

Norrie challenged the decision.

Last year, the New South Wales Court of Appeal found the existing law could recognise options other than male and female.

But the registrar will today ask the High Court to overturn that decision.

The case is being closely watched by other states and territories where similar laws are in place.

If the High Court upholds the appeal decision, that ruling could be binding for other jurisdictions.

Norrie is expected to be in the court for today's hearing.