In a landmark ruling, the top court overturned a lower court's ruling and sent the case for retrial. The female-to-male transsexual appealed to the court after his petition to change his gender in his family registry was rejected by two lower courts in 2003.

Many of the nation's estimated 30,000 transsexuals are likely to follow suit to be legally recognized as their chosen gender.

As Korean civil and family-registry laws have no clear definition of gender, courts have been issuing conflicting decisions over the recognition of transsexuals.

Some judges have taken the biological view that sex chromosomes determine gender and have refused to reflect the outcome of sex reassignment surgery on legal documents. Others have considered psychological and mental factors to be more important, granting legal recognition.

"If one is clearly recognizable as the opposite sex in both appearance and social life after having sex-change surgery, he or she has the right to pursue dignity, value and happiness as a human and live humanely," said Justice Kim Ji-hyung.

Yesterday's ruling had transgender advocates cheering and conservative religious activists fuming.

Choi Hyun-sook, representing a coalition of civic groups for the legal recognition of transsexuals, hailed the decision. "The court ruling gave hope to social minorities such as transsexuals and homosexuals. We will accelerate our efforts to enact a law facilitating gender change," she said.

Reverend Park Chong-soon of the Christian Council of Korea said the court's decision ran against public sentiment.

"If in court one is allowed to change legal gender because of a gender identity crisis or some factors in the surroundings, it will cause confusion in our society. Many Koreans, including me, have the urge to walk on the wild side now and then."

The recognition of transgender people has been a dilemma for the government and legal authorities since TV star and male-to-female transsexual Harisu brought the issue, long a social taboo, to the forefront.

A district court allowed the pop star to legally switch her gender from male to female in December 2002.