SINGAPORE, July 8 They wanted to look each other in the eye, they said, then pursue independent lives. And so Ladan and Laleh Bijani, the 29-year-old Iranian twins who were born joined at the head, asked doctors here to go ahead with an unprecedented operation to separate them that ultimately neither would survive.

The twin sisters died of blood loss this afternoon within 90 minutes of one another, doctors said, as a team of surgeons worked to separate their two brains.

"When we undertook this challenge, we knew the risks were great," said Dr. Loo Choon Yong, chairman of Raffles Hospital in Singapore, where the 50-hour operation took place.

The operation was the first known attempt to separate adult twins joined at the head. Similar separations have been performed successfully for decades on infants and, in 2001, doctors in Singapore succeeded in separating two infant Nepalese twins.

That operation placed Singapore and the neurosurgeon who led it, Dr. Keith Goh firmly on the map of cutting-edge medical centers.

As their operation neared, the Bijani sisters captured the attention and hopes of much of Singapore, which is still recovering from its battle against severe acute respiratory syndrome, the pneumonia-like disease that killed 32 people here.

News of the twins' deaths brought tears to the many well-wishers who had gathered for a prayer vigil outside the hospital since the operation began on Sunday.

Complicating the sisters' case was that their brains had grown closely intertwined over the years and shared a major vein. In 1996, German doctors had turned down their request for an operation, saying the shared vein made surgery too dangerous.

Doctors in Singapore, led by Dr. Goh, assembled a team of at least a dozen doctors and one hundred other medical professionals, including a noted American expert on such operations, Ben Carson, director of pediatric neurosurgery at Johns Hopkins Medical Institutions.

The twins asked doctors to go ahead with the operation even after being warned that there was at least a 50 percent chance that one or both would die or suffer severe brain damage. The case raised ethical questions within Singapore's medical community about whether doctors should allow patients to undergo such risky procedures, with some critics contending that doctors taking advantage of the sister's desperation.

Raffles Hospital convened an ethics committee to weigh such concerns and decided that the operation could proceed after determining that the twins were still willing after being made aware of the risks involved. In addition to physiotherapy sessions to prepare them for their surgery, the Bijanis met with counselors and psychologists.

The Bijanis explained their urgent desire to be separated at a news conference last month. "We are hoping the surgery will be successful," Ladan Bijani said. "We don't like to think about who will die or who should be saved."

Trained in Iran as lawyers, the sisters hoped to pursue individual careers after a recovery from surgery. While Ladan Bijani said she planned to continue in law, Laleh Bijani said she hoped to become a journalist.

With both sisters brains sharing one vein, surgeons fashioned a duplicate from a graft taken from Ladan's right thigh. While that procedure was apparently successful, doctors said the Bijanis' brains were more closely fused than they had expected.

As they toiled to separate the many tiny blood vessels connected the sisters' brains, however, the twins began to lose blood pressure. By 1:30 p.m. local time, doctors had managed to separate them, according to local news reports. But Ladan died an hour later. At 4 p.m., Laleh was also pronounced dead.

President S. R. Nathan of Singapore sent a letter of condolence to President Mohammad Khatami (news - web sites) of Iran and to the Iranian people, saying Singaporeans shared their loss. The twins' deaths also sparked mass outpourings of grief in Iran, where the Bijanis had gained national attention.

The Iranian government had offered to pay the estimated $300,000 cost of the operation. Some news reports, however, said Raffles Hospital had waived the cost of the operation. Hospital officials could not be reached for comment.

At their news conference in June, the Bijanis explained how, despite having lived every moment of their lives together, they had developed divergent interests. Laleh liked computer games, newspapers and books. Ladan like to chat on the Internet, read the Koran and pray. But one desire remained foremost, they told reporters at their news conference last month. "We want to see each other face to face," Laleh said. "We want to see each other," Ladan added, "without a mirror."

Why the heck didn't they get it done at birth? :\ First attempt at adult separation and FAILED. They would have had higher chances of survival at birth than 29 years later... sheesh