The court, responding to a request from an intersexual militant known as Alex Juergen, invoked the European Convention on Human Rights to insist that the legislature introduce the option of "other" or "inter" where civil register forms ask a person's gender.
"For the first time in my life, I feel like am being recognised as what I am, how I was born," said Alex Juergen, whose real identity remains a secret.
The constitutional court's decision was hailed by opposition social-democrat, liberal and ecology parties. However the far-right Freedom Party (FPOe), junior partner in Austria's coalition government, slammed the court's decision as "totally incomprehensible" saying it raises "numerous problems, notably concerning military service or retirement age."
The court stressed in its ruling that Article 8 of the European human rights convention guarantees the right to "an individual sexual identity" and protects "in particular, people with an alternative sexual identity".
The article in question states that "everyone has the right to respect for his private and family life".
Last November neighbouring Germany became the first European nation where the justice system called for the official recognition of a "third sex", a decision followed in May by the Netherlands.