Jake and Erin Herrin bid a tearful farewell to their conjoined twins Kendra and Maliyah, 4, before they were wheeled into an operating room Monday morning for a long and complex separation procedure.

This is the first effort to separate conjoined twins who share a kidney, the doctors said.

Kendra will receive the kidney, while Maliyah will be maintained on dialysis until she is strong enough to undergo a transplant procedure to receive one of her mother's kidneys.

Each girl will have one leg after the surgery, and the single liver and intestines will be divided between them. The surgeons intend to reconstruct the shared pelvis for each child.

The medical team will repair or remove several duplicate or undeveloped organs, a common occurrence with conjoined twins.

The children's parents, Jake and Erin Herrin, wrote on their family Web site of the girls' bravery and their own mixed feelings over separating the twins. "We are mourning their last day conjoined," they said.

Most conjoined twins do not survive long enough for separation surgery to be considered. In most cases, such procedures are carried out before the twins reach one year of age.

Physicians waited longer in the case of the Herrin twins because of the shared kidney. The blue-eyed blondes were excited about the surgery and showed no signs of anxiety, according to their parents.

The medical team carrying out the complex procedure consists of six surgeons, two anesthesiologists, one radiologist, two urologists and 25 to 30 support staff members.

Conjoined twins are rare, occurring only in one out of every 50,000 to 100,000 births.