BUENOS AIRES, Argentina - Activists say Argentina now leads the world in transgender rights after it granted people the right to change their legal and physical gender identity simply because they want to, without having to undergo judicial, psychiatric and medical procedures beforehand.

The gender identity law that won congressional approval with a 55-0 Senate vote Wednesday night is the latest in a growing list of bold moves on social issues by the Argentine government, which also legalized same-sex marriage two years ago. These changes primarily affect minority groups, but they are fundamental, President Cristina Fernandez has said, for a democratic society still shaking off the human-rights violations of the 1976-1983 dictatorship and the paternalism of the Roman Catholic Church.

Activists and academics who have tracked gender identity laws and customs worldwide said Thursday that no other country has gone so far to embrace gender self-determination. In the United States and Europe, transgender people must submit to physical and mental health exams and get past a series of other hurdles before getting sex-change treatments.

Argentina's law also is the first to give citizens the right to change their legal gender without first changing their bodies, said Justus Eisfeld, codirector of Global Action for Trans Equality in New York.

"The fact that there are no medical requirements at all - no surgery, no hormone treatment and no diagnosis - is a real game changer and completely unique in the world. It is light-years ahead of the vast majority of countries, including the U.S., and significantly ahead of even the most advanced countries," said Eisfeld, who researched the laws of the 47 countries for the Council of Europe's human rights commission.

Marcela Romero, who was born a man but got a sex-change operation 25 years ago, had to spend 10 years making his case in Argentina's courts before a judge ordered the civil registry to give her a new identity card listing her gender as female. "It's something humiliating . . . many of us have had to endure psychiatric and physical tests," she said Thursday. "With this law we'll no longer have to go through this."

Romero, 48, said she personally knows 40 people who had to get judicial approval for sex-change operations, and are still on waiting lists. The law should help them get the treatment they need, she said.

Romero leads the Argentine Transvestite, Transsexual and Transgender Association, whose legal team helped draft the law with help from an international coalition of activist groups pushing for governments to drop barriers to people determining their own gender identity. None of those groups has managed to find politicians willing to go as far as Argentina's, however.

This law is saying that we're not going to require you to live as a man or a woman, or to change your anatomy in some way. They're saying that what you say you are is what you are. And that's extraordinary," said Katrina Karkazis, a Stanford University bioethicist who wrote Fixing Sex, a study of the legal and medical boundaries around gender identity issues in the United States.

"Rather than our more sedimented ideas about what it is to be male or female, this sort of throws all of that up in the air in a really exciting way," she said.

Next up for Argentina's government is an overhaul of the country's civil and penal codes, an often-contradictory conglomeration of laws dating back nearly two centuries that cover all aspects of society.